Observed and projected functional reorganization of riverine fish assemblages from global change

Climate and land-use/land-cover change (“global change”) are restructuring biodiversity, globally. Broadly, environmental conditions are expected to become warmer, potentially drier (particularly in arid regions), and more anthropogenically developed in the future, with spatiotemporally complex effects on ecological communities. We used functional traits to inform Chesapeake Bay Watershed fish responses to future climate and land-use scenarios (2030, 2060, and 2090). We modeled the future habitat suitability of focal species representative of key trait axes (substrate, flow, temperature, reproduction, and trophic) and used functional and phylogenetic metrics to assess variable assemblage responses across physiographic regions and habitat sizes (headwaters through large rivers). Our focal species analysis projected future habitat suitability gains for carnivorous species with preferences for warm water, pool habitats, and fine or vegetated substrates. At the assemblage level, models projected decreasing habitat suitability for cold-water, rheophilic, and lithophilic individuals but increasing suitability for carnivores in the future across all regions. Projected responses of functional and phylogenetic diversity and redundancy differed among regions. Lowland regions were projected to become less functionally and phylogenetically diverse and more redundant while upland regions (and smaller habitat sizes) were projected to become more diverse and less redundant. Next, we assessed how these model-projected assemblage changes 2005–2030 related to observed time-series trends (1999–2016). Halfway through the initial projecting period (2005–2030), we found observed trends broadly followed modeled patterns of increasing proportions of carnivorous and lithophilic individuals in lowland regions but showed opposing patterns for functional and phylogenetic metrics. Leveraging observed and predicted analyses simultaneously helps elucidate the instances and causes of discrepancies between model predictions and ongoing observed changes. Collectively, results highlight the complexity of global change impacts across broad landscapes that likely relate to differences in assemblages' intrinsic sensitivities and external exposure to stressors.     

Excessive nitrogen and phosphorus in European rivers: 2000–2050

Rivers export nutrients to coastal waters. Excess nutrient export may result in harmful algal blooms and hypoxia, affecting biodiversity, fisheries, and recreation. The purpose of this study is to quantify for European rivers (1) the extent to which N and P loads exceed levels that minimize the risk of harmful algal blooms and (2) the relative shares of sources of N and P in rivers. This may help to identify effective management strategies to reduce coastal eutrophication. We focus on 48 rivers in 27 countries of the European Union (EU27). We used the Global Nutrient Export from Watersheds (NEWS) model to analyze nutrient export by rivers and the associated potentials for coastal eutrophication as reflected by Indicator for Coastal Eutrophication Potential (ICEP). In 2000, 38 of the 48 EU rivers indicated in our study had an ICEP > 0, indicating a relatively high potential for harmful algal blooms. These 38 rivers cover 60% of EU27 land area. Between 2000 and 2050 nutrient export by European rivers is projected to decrease. However, by 2050 still 34 EU rivers, covering 48% of the land area, have an ICEP > 0. This indicates that in these scenarios little progress is made in terms of environmental improvement. About one-third of the rivers with ICEP > 0 are N limited, and about two-thirds P limited. In N-limited rivers reducing N loads is a more effective way to reduce the risk for coastal eutrophication than reducing P, and vice versa. For N-limited rivers agriculture or sewage are the dominant sources of nutrients in river water. In P-limited rivers, sewage is found to be the dominant source of P, except for rivers draining into the Atlantic Ocean, where agriculture can also be dominant. A basin-specific approach is needed to effectively reduce N and P loads.     

Habitat fragmentation and extinction rates within freshwater fish communities: a faunal relaxation approach

Aim To estimate population extinction rates within freshwater fish communities since the fragmentation of palaeo‐rivers due to sea level rise at the end of the Pleistocene; to combine this information with rates estimated by other approaches (population surveys, fossil records); and to build an empirical extinction–area relationship. Location Temperate rivers from the Northern Hemisphere, with a special focus on rivers discharging into the English Channel, in north‐western France. Methods (1) French rivers. We used a faunal relaxation approach to estimate extinction rates in coastal rivers after they became isolated by the sea level rise. Tributaries within the Seine were used to build a species–area relationship for a non‐fragmented river system to predict species richness in coastal rivers before their fragmentation. (2) Other rivers. Extinction rates obtained for four other Holarctic river systems fragmented at the end of the Pleistocene, the fragmented populations of one salmonid species (Japan) and the fossil records from the Mississippi Basin were included in the study. Results (1) French rivers. Within strictly freshwater fish species, rare and/or habitat specialist species were the most affected by fragmentation. In contrast, euryhaline species were not affected. A negative relationship between extinction rate and river basin size was observed. (2) Other rivers. Our study established a common scaling relationship for freshwater fish population extinction rates that spans seven orders of magnitude in river basin size. Main conclusions This study strongly suggests that extinctions of fish populations occurred within French coastal rivers after they became isolated 8000 years ago. The patterns observed at regional and inter‐continental scales are consistent with the expectation that large populations are less prone to extinction than small ones, resulting in a strong extinction–area relationship coherent over a large spatio‐temporal scale. Our study is the first multi‐scale quantitative assessment of background extinction patterns for freshwater fishes.     

Structural and functional characteristics of the bacterioplankton of rivers flowing through a large city (Cherepovets,Upper Volga Region)

The structural and functional properties of the bacterioplankton in two small rivers and the Sheksna River that run through the large industrial city of Cherepovets were studied from April to October 2009–2011. The three-year average numbers and biomass of planktonic bacteria in small rivers were 18.7–18.8 million cells/mL and 3.5–4.9 g/m³, respectively; these values in the Sheksna River’s littoral zone were 15.8 million cells/mL and 2.2 g/m³. The bacterioplankton production in the small water courses exceeded that in the Sheksna River by a factor of 1.8–2.2. The contribution of bacterial filaments to the total biomass and the total bacterioplankton production increases in small polluted rivers.     

Spatial modeling of deforestation processes in the Central Peruvian Amazon

This study examines the relation between primary forest loss and landscape characteristics in the Ucayali region, Peru. Seven variables (rivers, elevation, annual precipitation, soil suitability for agriculture, population density, paved roads, and unpaved roads), were identified as potential deforestation drivers. The variables were converted into spatially explicit layers of continuous data and divided into a 9 km² grid. A multiple regression analysis was conducted to determine variable significance. Distance to paved and unpaved roads were strongly associated with deforestation, followed by distance to rivers, annual precipitation and elevation. All significant variables were negatively correlated with deforestation. Variables excluded from the model were population density and soil suitability for agriculture, suggesting that the influence of population density on forest clearing across the study area was not significant, and that deforestation activities were undertaken regardless whether soils are suitable for agriculture or not. Based on the linear regression analysis, the significant variables were selected and added to the Land Change Modeler in order to project primary forest coverage by 2025. The modeling results predict extensive deforestation along the Aguaytia River and at the forest/non-forest interface along the paved highway. The rate of primary forest removal is expected to increase from 4783 ha y⁻¹ (for the 2007–2014 period) to 5086 ha y⁻¹ (for the 2015–2025 period). A preliminary survey questionnaire conducted to explore deforestation intentions by farmers in the region, partly confirmed the overall deforestation trends as projected by the model.     

Seasonal and interannual variation of bacterial production in lowland rivers of the Orinoco basin

1. We examined the influence of hydrologic seasonality on temporal variation of planktonic bacterial production (BP) in relatively undisturbed lowland rivers of the middle Orinoco basin, Venezuela. We sampled two clearwater and two blackwater rivers over 2 years for dissolved organic carbon (DOC), chlorophyll, phosphorus and bacterial abundance to determine their relationship to temporal variation in BP. 2. Dissolved organic carbon concentration was greater in blackwater (543–664 μm ) than in clearwater rivers (184–240 μm ), and was generally higher during periods of rising and high water compared with low water. Chlorophyll concentration peaked (3 μg L^?1) during the first year of study when discharge was lowest, particularly in blackwater rivers. Soluble reactive phosphorus (SRP) was very low in the study rivers (<3.8 μg L^?1) and concentration increased during low water. 3. Average BP was higher in clearwater (0.20–0.26 μg C L^?1 h^?1) than in blackwater rivers (0.14–0.17 μg C L^?1 h^?1), although mean bacterial abundance was similar among rivers (0.6–0.8 × 10⁶ cells mL^?1). 4. Periods of higher chlorophyll a concentration (low water) or flushing of terrestrial organic material (rising water) were accompanied by higher BP, while low BP was observed during the period of high water. 5. Interannual variation in BP was influenced by variations in discharge related to El Niño Southern Oscillation events. 6. Seasonal variation in BP in the study rivers and other tropical systems was relatively small compared with seasonal variation in temperate rivers and lakes. In addition to the low seasonal variation of temperature in the tropics, low overall human disturbance could result in less variation in the inputs of nutrients and carbon to the study rivers compared with more disturbed temperate systems.     

Unique microbiome in organic matter–polluted urban rivers

Approximately half of the global annual production of wastewater is released untreated into aquatic environments, which results in worldwide organic matter pollution in urban rivers, especially in highly populated developing countries. Nonetheless, information on microbial community assembly and assembly-driving processes in organic matter–polluted urban rivers remains elusive. In this study, a field study based on water and sediment samples collected from 200 organic matter–polluted urban rivers of 82 cities in China and Indonesia is combined with laboratory water-sediment column experiments. Our findings demonstrate a unique microbiome in these urban rivers. Among the community assembly-regulating factors, both organic matter and geographic conditions play major roles in determining prokaryotic and eukaryotic community assemblies, especially regarding the critical role of organic matter in regulating taxonomic composition. Using a dissimilarity-overlap approach, we found universality in the dynamics of water and sediment community assembly in organic matter–polluted urban rivers, which is distinctively different from patterns in eutrophic and oligotrophic waters. The prokaryotic and eukaryotic communities are dominated by deterministic and stochastic processes, respectively. Interestingly, water prokaryotic communities showed a three-phase cyclic succession of the community assembly process before, during, and after organic matter pollution. Our study provides the first large-scale and comprehensive insight into the prokaryotic and eukaryotic community assembly in organic matter–polluted urban rivers and supports their future sustainable management.     

Methane emissions from Amazonian Rivers and their contribution to the global methane budget

Methane (CH₄) fluxes from world rivers are still poorly constrained, with measurements restricted mainly to temperate climates. Additional river flux measurements, including spatio‐temporal studies, are important to refine extrapolations. Here we assess the spatio‐temporal variability of CH₄ fluxes from the Amazon and its main tributaries, the Negro, Solimões, Madeira, Tapajós, Xingu, and Pará Rivers, based on direct measurements using floating chambers. Sixteen of 34 sites were measured during low and high water seasons. Significant differences were observed within sites in the same river and among different rivers, types of rivers, and seasons. Ebullition contributed to more than 50% of total emissions for some rivers. Considering only river channels, our data indicate that large rivers in the Amazon Basin release between 0.40 and 0.58 Tg CH₄ yr^?1. Thus, our estimates of CH₄ flux from all tropical rivers and rivers globally were, respectively, 19–51% to 31–84% higher than previous estimates, with large rivers of the Amazon accounting for 22–28% of global river CH₄ emissions.     

Influence of large South American rivers of the Plata Basin on distributional patterns of tropical snakes: a panbiogeographical analysis

Aim The main drainages of the Plata Basin – the Paraná, Paraguay and Uruguay rivers – begin in tropical latitudes and run in a north–south direction into subtropical–temperate latitudes. Consequently, the biota of these rivers has tropical elements that contrast with temperate biomes through which the rivers run. We apply a panbiogeographical approach, to test whether the large rivers of the Plata Basin have a differential influence on distributional patterns of tropical snakes in subtropical and temperate latitudes of South America. Location Subtropical and temperate sections of the major Plata Basin rivers, South America. Methods We compared the individual tracks of 94 snake taxa. The track analysis consisted of: (1) plotting the localities of each taxon on maps, (2) connecting the localities of each taxon using a minimal geographical proximity determinant of the ‘individual tracks’, and (3) superimposing the individual tracks to determine generalized tracks. To detect tropical snakes that reach higher latitudes through the rivers we used the preferential direction of distribution concept. For each taxon we measured the angular deviations between the line of its individual track and the course of the rivers in a 100 × 100 km scaled grid. Average angular values < 45° indicated a positive association with the rivers. Results Thirty‐five of 94 taxa showed distributions associated with the major rivers of the Plata Basin, including fauna from distinct biogeographical lineages, supported by the occurrence of five generalized tracks as follows: (1) the Paraguay–Middle Paraná, (2) the Paraguay–Paraná fluvial axis, Upper Paraná and Middle Paraná to Upper Delta, (3) the Lower Paraguay, Paraná and Uruguay rivers, excluding the sectors High Paraná and High Uruguay, (4) the Uruguay River and Upper Paraná, and (5) the High Paraná. The Atlantic species occurred with significantly higher frequency in the Uruguay River and High Paraná river sections, the Amazon species were found with significantly higher frequency in the Paraguay and Middle Paraná sections, and the species with a Pantanal distribution were found in all sections. Main conclusions The observed distributional patterns may be explained by the interaction of ecological, geographical and historical factors. Previous authors have developed ecological (hydrological or environmental similarity) or dispersalist (effect of rivers as migration routes) explanations. The coincidence between generalized tracks and past geomorphological events that caused displacements and changed relationships between the Paraguay, Paraná and Uruguay river sections supports hypotheses involving the strong influence of historical factors in the present configuration of tropical snake distribution in temperate latitudes.     

Comparing urbanization patterns in Guangzhou of China and Phoenix of the USA: The influences of roads and rivers

Examining the similarities and differences in urbanization pattern between cities in developed and developing countries may enhance our understanding of urbanization processes and mechanisms. Using a buffer analysis approach, we compared the long-term spatiotemporal patterns of urbanization between Guangzhou of China and Phoenix of the United States during the 20th century, with a particular emphasis on the impacts of major roads and rivers. The development of Guangzhou was relatively compact, whereas the development of Phoenix was much more dispersed. The two metropolitan areas were characterized mainly by two types of urban expansion processes. Guangzhou experienced a diffusion–coalescence–diffusion–coalescence process while Phoenix experienced a diffusion–coalescence process. The buffer analysis indicated that the impacts of roads and rivers on the urbanization of Guangzhou and Phoenix were similar in terms of urban area, the number of urban patches, the mean patch size, but different in terms of the complexity of urban patches. The urban area declined with increasing distances to roads, but it increased when the distance was close to the rivers and then declined with the increment of distances to rivers. In general, the impacts of roads are stronger in Phoenix than in Guangzhou, while the impacts of rivers are greater in Guangzhou than in Phoenix. These similarities and differences between the two metropolitan regions are reflective of those in both physical conditions and land use policies in the two countries. By comparing these similarities and differences, we can improve our understanding of the urbanization processes in both developed and developing countries, which is necessary for achieving global urban sustainability.     

Zooplankton of turbid and hydrologically dynamic prairie rivers

1. Compared with rivers in more humid, forested ecoregions of eastern and midwestern U.S.A., rivers in semi‐arid grassland of the U.S. Great Plains tend to be relatively shallow, more variable in discharge, and characterised by high suspended sediment loads. Although critical life stages of fish in prairie rivers probably depend at least partially on zooplanktonic food, data on community and distributional patterns of potamoplankton in these widespread ecosystems are almost entirely absent. 2. We examined summer zooplankton distribution in five prairie rivers (Arkansas, Kansas, Platte, Elkhorn, and Niobrara Rivers) spread over six degrees of latitude during 2003–2004. We compared our results from 126 samples with previously collected data from the Ohio and St Lawrence Rivers in forested ecoregions and correlated differences with abiotic environmental conditions. 3. The importance of hydrological retention zones to stream biota has been recently demonstrated for rivers with quasi‐permanent islands and slackwater regions, but the importance of slackwaters formed by ephemeral sandbar islands in prairie rivers is unknown. We evaluated the role of hydrological retention for planktonic rotifers, cladocera, and copepods in the Kansas River during the summer of 2004. 4. Zooplankton assemblages were extremely similar among prairie rivers (Sorensen Dissimilarity Index: mean = 0.07) but moderately disparate for comparisons of prairie versus forested‐basin rivers (mean = 0.50). 5. Total zooplankton densities in prairie rivers (approximately 81 L^?1) were intermediate between the Ohio (approximately 92 L^?1) and St Lawrence Rivers (approximately 43 L^?1), but relative abundances were significantly different. Rotifers represented >99% of zooplankton individuals in grassland rivers, but only approximately 37–68% in other rivers. Rotifer species richness was lower in prairie rivers, but relative abundances of common genera were much less skewed compared with eastern rivers where Polyarthra dominated rotifer assemblages (41–73%). 6. For comparisons among rivers, rotifers were significantly more abundant in turbid rivers, while microcrustaceans were less dense. However, for comparisons within the Kansas River over time, rotifer densities were inversely related to turbidity. We hypothesise that rotifers indirectly benefit from river turbidity because their food competitors (cladocera) and predators (e.g. cyclopoid copepods and visually feeding fish) are relatively more susceptible to suspended sediments. 7. Crustacean densities were positively related to the degree of hydrological retention (negatively to current velocities) throughout the study, but rotifer densities were significantly depressed by current velocities only when river discharge was high, making slackwaters that much more valuable. Ephemeral sandbars may not provide sufficient hydrological retention in time and space to sustain viable crustacean populations, but they are adequate to help sustain growth of rotifer populations.     

Modelling distribution in European stream macroinvertebrates under future climates

Climate change is predicted to have profound effects on freshwater organisms due to rising temperatures and altered precipitation regimes. Using an ensemble of bioclimatic envelope models (BEMs), we modelled the climatic suitability of 191 stream macroinvertebrate species from 12 orders across Europe under two climate change scenarios for 2080 on a spatial resolution of 5 arc minutes. Analyses included assessments of relative changes in species’ climatically suitable areas as well as their potential shifts in latitude and longitude with respect to species’ thermal preferences. Climate‐change effects were also analysed regarding species’ ecological and biological groupings, namely (1) endemicity and (2) rarity within European ecoregions, (3) life cycle, (4) stream zonation preference and (5) current preference. The BEMs projected that suitable climate conditions would persist in Europe in the year 2080 for nearly 99% of the modelled species regardless of the climate scenario. Nevertheless, a decrease in the amount of climatically suitable areas was projected for 57–59% of the species. Depending on the scenario, losses could be of 38–44% on average. The suitable areas for species were projected to shift, on average, 4.7–6.6° north and 3.9–5.4° east. Cold‐adapted species were projected to lose climatically suitable areas, while gains were expected for warm‐adapted species. When projections were analysed for different species groupings, only endemics stood out as a particular group. That is, endemics were projected to lose significantly larger amounts of suitable climatic areas than nonendemic species. Despite the uncertainties involved in modelling exercises such as this, the extent of projected distributional changes reveals further the vulnerability of freshwater organisms to climate change and implies a need to understand the consequences for ecological function and biodiversity conservation.     

The ‘wet–dry’ in the wet–dry tropics drives river ecosystem structure and processes in northern Australia

1. Northern Australia is characterised by a tropical wet–dry climate that regulates the distinctive character of river flow regimes across the region. There is marked hydrological seasonality, with most flow occurring over only a few months of the year during the wet season. Flow is also characterised by high variability between years, and in the degree of flow cessation, or intermittency, over the dry season. 2. At present, the relatively low human population density and demand for water in the region means that most rivers have largely unmodified flow regimes. These rivers therefore provide a good opportunity to understand the role of natural flow variability in river ecosystem structure and processes. 3. This review describes the major flow regime classes characterising northern Australian rivers, from perennial to seasonally intermittent to extremely intermittent, and how these regimes give rise to marked differences in the ecological character of these tropical rivers, particularly their floodplains. 4. We describe the key features of these flow regimes, namely the wet and dry seasons and the transitions between these seasons, and how they regulate the biophysical heterogeneity, primary productivity and movement of biota in Australia’s wet–dry tropical rivers. 5. We develop a conceptual model that predicts the likely hydrological and ecological consequences of future increases in water abstraction (e.g. for agriculture), and suggest how such impacts can be managed so that the distinctive ecological character of these rivers is maintained.     

Forecasting changes in water quality in rivers associated with growing biofuels in the Arkansas-White-Red river drainage,USA

Excess nutrients from agriculture in the Mississippi River drainage, USA have degraded water quality in freshwaters and contributed to anoxic conditions in downstream estuaries. Consequently, water quality is a significant concern associated with conversion of lands to bioenergy production. This study focused on the Arkansas-White-Red river basin (AWR), one of five major river basins draining to the Mississippi River. The AWR has a strong precipitation gradient from east to west, and advanced cellulosic feedstocks are projected to become economically feasible within normal-to-wet areas of the region. In this study, we used large-scale watershed modeling to identify areas along this precipitation gradient with potential for improving water quality. We compared simulated water quality in rivers draining projected future landscapes with and without cellulosic bioenergy for two future years, 2022 and 2030 with an assumed farmgate price of $50 per dry ton. Changes in simulated water quantity and quality under future bioenergy scenarios varied among subbasins and years. Median water yield, nutrient loadings, and sediment yield decreased by 2030. Median concentrations of nutrients also decreased, but suspended sediment, which is influenced by decreased flow and in-stream processes, increased. Spatially, decreased loadings prevailed in the transitional ecotone between 97° and 100° longitude, where switchgrass, Panicum virgatum L., is projected to compete against alternative crops and land uses at $50 per dry ton. We conclude that this region contains areas that hold promise for sustainable bioenergy production in terms of both economic feasibility and water quality protection.     

The Mediterranean Sea as a ‘cul‐de‐sac’ for endemic fishes facing climate change

The Mediterranean Sea is a hotspot of biodiversity, and climate warming is expected to have a significant influence on its endemic fish species. However, no previous studies have predicted whether fish species will experience geographic range extensions or contractions as a consequence of warming. Here, we projected the potential future climatic niches of 75 Mediterranean Sea endemic fish species based on a global warming scenario implemented with the Mediterranean model OPAMED8 and a multimodel inference, which included uncertainty. By 2070–2099, the average surface temperature of the Mediterranean Sea was projected to warm by 3.1 °C. Projections for 2041–2060 are that 25 species would qualify for the International Union for the Conservation of Nature and Natural Resources (IUCN) Red List, and six species would become extinct. By 2070–2099, 45 species were expected to qualify for the IUCN Red List whereas 14 were expected to become extinct. By the middle of the 21st century, the coldest areas of the Mediterranean Sea (Adriatic Sea and Gulf of Lion) would act as a refuge for cold‐water species, but by the end of the century, those areas were projected to become a ‘cul‐de‐sac’ that would drive those species towards extinction. In addition, the range size of endemic species was projected to undergo extensive fragmentation, which is a potentially aggravating factor. Since a majority of endemic fishes are specialists, regarding substratum and diet, we may expect a reduced ability to track projected climatic niches. As a whole, 25% of the Mediterranean Sea continental shelf was predicted to experience a total modification of endemic species assemblages by the end of the 21st century. This expected turnover rate could be mitigated by marine protected areas or accelerated by fishing pressure or competition from exotic fishes. It remains a challenge to predict how these assemblage modifications might affect ecosystem function.     

How climate,migration ability and habitat fragmentation affect the projected future distribution of European beech

Recent efforts to incorporate migration processes into species distribution models (SDMs) are allowing assessments of whether species are likely to be able to track their future climate optimum and the possible causes of failing to do so. Here, we projected the range shift of European beech over the 21st century using a process‐based SDM coupled to a phenomenological migration model accounting for population dynamics, according to two climate change scenarios and one land use change scenario. Our model predicts that the climatically suitable habitat for European beech will shift north‐eastward and upward mainly because (i) higher temperature and precipitation, at the northern range margins, will increase survival and fruit maturation success, while (ii) lower precipitations and higher winter temperature, at the southern range margins, will increase drought mortality and prevent bud dormancy breaking. Beech colonization rate of newly climatically suitable habitats in 2100 is projected to be very low (1–2% of the newly suitable habitats colonised). Unexpectedly, the projected realized contraction rate was higher than the projected potential contraction rate. As a result, the realized distribution of beech is projected to strongly contract by 2100 (by 36–61%) mainly due to a substantial increase in climate variability after 2050, which generates local extinctions, even at the core of the distribution, the frequency of which prevents beech recolonization during more favourable years. Although European beech will be able to persist in some parts of the trailing edge of its distribution, the combined effects of climate and land use changes, limited migration ability, and a slow life‐history are likely to increase its threat status in the near future.     

Assessment of the Genotoxic Potential of Sediments Contaminated with POPs and Agricultural Soils Using Vicia faba Micronucleus Assay

The aim of this study was to assess the levels of some persistent organic pollutants in the surface sediments from the Zahuapan and Atoyac rivers (Tlaxcala, Mexico), as well as to determine the genotoxic potential, by the micronucleus test in Vicia faba, of the sediments and agricultural soils irrigated with water from these rivers. This document is the first study on the presence of POPs in surface sediments of the above-mentioned rivers; among the compounds analyzed are the HCH isomers, DDT and its metabolite DDE, HCB, mirex, aldrin, and 41 PCB congeners. The concentrations of HCB, ΣDDTs, ΣHCHs, and ΣPCBs ranged from 138–510, 45–450, 3–27, and 59–1876 μg kg^?1 dry weight, respectively. The highest levels of HCB, HCH isomers, and PCB congeners were found in the Atoyac River, and these compounds have the potential for causing an environmental impact. On the other hand, biological testing shows that both sediments and agricultural soils possess a genotoxic potential, given that the micronuclei frequency in V. faba is increased.     

The impact of projected increases in urbanization on ecosystem services

Alteration in land use is likely to be a major driver of changes in the distribution of ecosystem services before 2050. In Europe, urbanization will probably be the main cause of land-use change. This increase in urbanization will result in spatial shifts in both supplies of ecosystem services and the beneficiaries of those services; the net outcome of such shifts remains to be determined. Here, we model changes in urban land cover in Britain based on large (16%) projected increases in the human population by 2031, and the consequences for three different services--flood mitigation, agricultural production and carbon storage. We show that under a scenario of densification of urban areas, the combined effect of increasing population and loss of permeable surfaces is likely to result in 1.7 million people living within 1 km of rivers with at least 10 per cent increases in projected peak flows, but that increasing suburban 'sprawl' will have little effect on flood mitigation services. Conversely, losses of stored carbon and agricultural production are over three times as high under the sprawl as under the 'densification' urban growth scenarios. Our results illustrate the challenges of meeting, but also of predicting, future demands and patterns of ecosystem services in the face of increasing urbanization.     

Life history and reproductive capacity of Gammarus fossarum and G. roeseli (Crustacea: Amphipoda) under naturally fluctuating water temperatures: a simulation study

SUMMARY 1. Mathematical functions developed in long‐term laboratory experiments at different constant temperatures were combined with daily water temperatures for 1991–93 in eight Austrian streams and rivers to simulate the complex life histories and reproductive capacities of two freshwater amphipods: Gammarus fossarum and G. roeseli. The functions describe brood development times, hatching success, times taken to reach sexual maturity, growth, and fecundity. The sex ratio was assumed to be 0.5 and an autumn–winter reproductive resting period was based on observations of six river populations. Simulations included summer‐cold mountain streams, summer‐warm lowland rivers, watercourses fed by groundwater or influenced by heated effluents, and varying amplitudes of change within each year. 2. A fortran 77 computer program calculated growth from birth to sexual maturity of first‐generation females born on the first day of each calendar month in 1991, and the numbers of offspring successfully released from the maternal broodpouch in successive broods. At the 1991–93 regimes of temperature, individual G. fossarum released 127–208 offspring and G. roeseli released 120–169 in seven or eight successive broods during life spans of less than 2 years in six rivers. Life spans extended into a third year in the relatively cool River Salzach (mean temperature 7.5 °C). They were not completed in the very cold River Steyr (mean 5.6, range 2.5–7.9 °C), where G. fossarum produced five broods (totalling 120 offspring) and G. roeseli only two broods (totalling 28 offspring) in the 3‐year period. Except in the Steyr, some offspring grew rapidly to maturity and produced several second‐generation broods during the simulation period; in the warmest rivers some third‐generation broods were also produced. Birth dates, early or late in the year, influenced the subsequent production of broods and young, depending on temperature regimes in particular rivers. Total numbers of offspring produced by the second and third generations represent the theoretical reproductive capacities of G. fossarum and G. roeseli. Minimum and maximum estimates mostly ranged from 100 to 17 300, were larger for G. fossarum except in the warmest river (March), where temperatures rose above 20 °C for 56–78 days in summer, and largest (maximum 37 600) in the River Voeckla heated by discharge from a power‐station (mean 11.5 °C). Results from the simulations agree with preliminary assessments of relative abundances for G. fossarum and G. roeseli in several of the study rivers, but in some one or both species appear to be absent. On a wider scale, the present study confirms that G. fossarum is potentially more successful than G. roeseli in cool rivers but indicates that neither species is likely to maintain viable populations in cold rivers strongly influenced by snow and ice‐melt. 3. The potential impacts of future river warming by increases of 1, 2 and 3 °C, due to climate change, vary according to river site, date of fertilisation, the extent of temperature increase, and the species of Gammarus. For Austrian rivers with mean temperatures in the range c. 7–10 °C, future warming would result in modest changes in the life histories and reproductive capacities of both G. fossarum and G. roeseli; the former would find improved temperature conditions in watercourses that are currently very cold throughout the year, and both would find warm rivers less tolerable. 4. The high potential reproductive capacity of gammarids, with rapid production of numerous successive broods when sexual maturity is finally achieved, indicates adaptation to high mortality during the relatively long period of growth to sexual maturity, and provides scope for an opportunistic strategy of emigration from centres of population abundance to colonise new territory when conditions are favourable. Rapid expansion of populations is desirable to combat the effects of environmental catastrophes, both frequent and short‐term floods and droughts, and more long‐term climatic changes that have occurred several times in glacial–interglacial periods during the current Ice Age.     

Mechanistic insights into the effects of climate change on larval cod

Understanding the biophysical mechanisms that shape variability in fisheries recruitment is critical for estimating the effects of climate change on fisheries. In this study, we used an Earth System Model (ESM) and a mechanistic individual‐based model (IBM) for larval fish to analyze how climate change may impact the growth and survival of larval cod in the North Atlantic. We focused our analysis on five regions that span the current geographical range of cod and are known to contain important spawning populations. Under the SRES A2 (high emissions) scenario, the ESM‐projected surface ocean temperatures are expected to increase by >1 °C for 3 of the 5 regions, and stratification is expected to increase at all sites between 1950–1999 and 2050–2099. This enhanced stratification is projected to decrease large (>5 μm ESD) phytoplankton productivity and mesozooplankton biomass at all 5 sites. Higher temperatures are projected to increase larval metabolic costs, which combined with decreased food resources will reduce larval weight, increase the probability of larvae dying from starvation and increase larval exposure to visual and invertebrate predators at most sites. If current concentrations of piscivore and invertebrate predators are maintained, larval survival is projected to decrease at all five sites by 2050–2099. In contrast to past observed responses to climate variability in which warm anomalies led to better recruitment in cold‐water stocks, our simulations indicated that reduced prey availability under climate change may cause a reduction in larval survival despite higher temperatures in these regions. In the lower prey environment projected under climate change, higher metabolic costs due to higher temperatures outweigh the advantages of higher growth potential, leading to negative effects on northern cod stocks. Our results provide an important first large‐scale assessment of the impacts of climate change on larval cod in the North Atlantic.