Longitudinal Spatial Patterns of Bacterial Production and Respiration in a Large River–Estuary: Implications for Ecosystem Carbon Consumption

Rivers and estuaries transport organic carbon (C) from terrestrial and freshwater ecosystems to the marine environment. During this transit, bacteria actively utilize and transform organic C, but few studies have measured detailed spatial variation in rates of bacterial respiration (BR) and production (BP). We measured BP at 39 stations and BR at 12 stations at monthly intervals along a 200-km reach of the tidal Hudson River. We observed strong repeatable spatial patterns for both BP and BR, with rates declining in the downstream direction. Bacterial Production had much greater dynamic range of spatial variation than BR. We used the detailed seasonal and spatial data on BP and BR to measure the total C demand of bacteria at several scales. We calculated volumetric and areal rates for 12 sections of the Hudson, as well as the total C utilization. Volumetric BR averaged 20 g-C-m^–3 y^–1, but it was highest in the most upstream section at 30 g C m^–3 y^–1. Areal rates averaged over the entire river were 174 g C m^–2 y^–1, but they were 318 g C m^–2 y^–1 in the deepest section of the river, indicating the importance of morphometric variation. Total bacterial C demand increased downriver with increasing total volume. Overall, bacteria in the freshwater section of the river consumed approximately 18–25.5 × 10⁹ g C y^–1, about 20% of the total organic C load.     

Feeding habits of the exotic black bullhead Ameiurus melas (Rafinesque) in the Iberian Peninsula: first evidence of direct predation on native fish species

The feeding ecology of the exotic invasive black bullhead Ameiurus melas was conducted in the Iberian Peninsula for the first time. Dietary analysis based on the stomach contents of individuals caught in several Iberian basins was carried out as a first step to evaluate its potential threat for the native Iberian ichthyofauna. Aquatic macroinvertebrates (mainly Chironomidae) dominated the black bullhead's diet in all size-classes and sites, irrespective of natural riverine or artificial lentic habitats. Secondary prey items were responsible for the observed between-sites (microcrustaceans in artificial lentic habitat; oligochaeta and caddisfly larvae in natural riverine habitats) and ontogenetic diet differences (from microcrustaceans to larger prey). These diet variations were also detected in trophic diversity values and feeding strategy plots. Black bullheads consumed plant material, terrestrial prey and co-occurring fish species (native or exotic) and thus they could be considered as generalist or opportunistic, foraging on the most abundant and available prey. There was no positive relationship between black bullhead size (total length) and fish prey size, probably indicating piscivory on dead or dying vulnerable fishes as well as predation on smaller-sized active fishes. The results showed that the black bullhead could negatively affect native Iberian ichthyofauna throughout direct predation and competition. Aspects of potential conservation and management implications of fishes resulting from the undesirable presence of the black bullhead in Iberian water bodies are discussed.     

Occurrence,distribution and transport of pesticides into the Salton Sea Basin,California, 2001–2002

The Salton Sea is a hypersaline lake located in southeastern California. Concerns over the ecological impacts of sediment quality and potential human exposure to dust emissions from exposed lakebed sediments resulting from anticipated shrinking of shoreline led to a study of pesticide distribution and transport within the Salton Sea Basin, California, in 2001–2002. Three sampling stations—upriver, river mouth, and offshore—were established along each of the three major rivers that discharge into the Salton Sea. Large-volume water samples were collected for analysis of pesticides in water and suspended sediments at the nine sampling stations. Samples of the bottom sediment were also collected at each site for pesticide analysis. Sampling occurred in October 2001, March–April 2002, and October 2002, coinciding with the regional fall and spring peaks in pesticide use in the heavily agricultural watershed. Fourteen current-use pesticides were detected in water and the majority of dissolved concentrations ranged from the limits of detection to 151 ng/l. Diazinon, EPTC and malathion were detected at much higher concentrations (940–3,830 ng/l) at the New and Alamo River upriver and near-shore stations. Concentrations of carbaryl, dacthal, diazinon, and EPTC were higher in the two fall sampling periods, whereas concentrations of atrazine, carbofuran, and trifluralin were higher during the spring, which matched seasonal use patterns of these pesticides. Current-use pesticides were also detected on suspended and bed sediments in concentrations ranging from detection limits to 106 ng/g. Chlorpyrifos, dacthal, EPTC, trifluralin, and DDE were the most frequently detected pesticides on sediments from all three rivers. The number of detections and concentrations of suspended sediment-associated pesticides were often similar for the river upriver and near-shore sites, consistent with downstream transport of pesticides via suspended sediment. While detectable suspended sediment pesticide concentrations were more sporadic than detected aqueous concentrations, seasonal trends were similar to those for dissolved concentrations. Generally, the pesticides detected on suspended sediments were the same as those on the bed sediments, and concentrations were similar, especially at the Alamo River upriver site. With a few exceptions, pesticides were not detected in suspended or bed sediments from the off-shore sites. The partitioning of pesticides between water and sediment was not predictable from solely the physical–chemical properties of individual pesticide compounds, but appear to be a complicated function of the quantity of pesticide applied in the watershed, residence time of sediments in the water, and compound solubility and hydrophobicity. Sediment concentrations of most pesticides were found to be 100–1,000 times lower than the low-effects levels determined in human health risk assessment studies. However, maximum concentrations of chlorpyrifos on suspended sediments were approximately half the low-effects level, suggesting the need for further sediment characterization of lake sediments proximate to riverine inputs. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005     

Determining discharges from the Table Mountain Group (TMG) aquifer to wetlands in the Southern Cape, South Africa

The focus of this study was to determine whether coastal wetlands in lowland settings could be dependent on groundwater from the deep circulating confined Table Mountain Group (TMG) aquifer. Groundwater interactions with wetlands are normally perceived to be limited to primary aquifers. A comparative study was done between two endorheic coastal wetlands in the southern Cape. Earlier reports stated that these groundwater dependent wetlands were fed by discharges from the fixed dunes surrounding them. On the basis of a three-dimensional electrical conductivity (EC) interpolation for Groenvlei, a hydrological link between the TMG aquifer and Groenvlei and Van Kervelsvlei was investigated by measuring water level and quality of groundwater and surface water. Water quality parameters used were EC, pH, Na⁺, Fe²⁺ and Cl⁻. The results from this, and an accompanying study, on the basis of water quality and plant nutrient cycling assessments, indicated direct groundwater discharges from the TMG to at least Van Kervelsvlei, with Groenvlei receiving secondary discharges from the TMG via Van Kervelslvlei. These findings significantly affect the current knowledge on which water balance models are based for the determination of groundwater availability for the area. Handling editor: D. Hamilton The first author did the research as part of his PhD in the Department of Earth Sciences of the University of the Western Cape, Bellville, South Africa. Funding is quoted under acknowledgements.     

Multi-attribute ecological river typology for assessing ecological condition and conservation planning

A river classification framework is needed to make good management and planning decisions about river health and biodiversity. We developed a multi-attribute ecological river typology to address this need in the Australian State of New South Wales (801,428 km²). Multivariate patterns in data collected from 322 reference sites were used to define river types for each attribute: abiotic features (10 types), fish assemblages (6 types) and macroinvertebrate assemblages from river edges (8 types) and riffle zones (5 types). We used classification tree analysis to define broad regions for each attribute and then to construct identification keys for river types within each region using slope, elevation, maximum distance from source, latitude and mean annual rainfall. These keys allow the mapping of the likely spatial extent of river types and the assignment of a multi-attribute river-type identity to a river reach anywhere in the State. We used the average dissimilarity distances among the river types and the rates of misclassification of reference sites to assess the reliability of the assignments for different attributes in different regions. This approach to river classification can be applied anywhere in the world, resulting in simple to highly complex typologies depending on data availability. In data-poor areas it may result in a single attribute typology based on remotely derived variables and a coarsely defined reference condition. In data-rich areas the typology may have a large number of attributes using very large datasets with high resolution. Handling editor: D. Dudgeon     

Assessing the efficiency of connectivity measures with regard to the EU-Water Framework Directive in a Danube-tributary system

The effect of restoring connectivity for fish by the construction of 11 fish ladders in the Pielach and Melk rivers, both tributaries to the Danube in Austria, was monitored using electric fishing and fish traps between 1999 and 2004. In order to assess the efficiency of connectivity rehabilitation measures pre- and post-project data combining electric fishing and trap catch data were analyzed by means of three fish-based assessment methods: a MUlti-Level concept for a Fish-based, river-type-specific Assessment of ecological integrity (MULFA), the Fish Index Austria (FIA) and the European Fish Index (EFI). The effect of adding qualitative trap catch data to electric fishing data on metrics and indices was also tested and the magnitude of the effect was related to the distance of the sites from the river mouth. The results clearly demonstrated the significant contribution of connectivity rehabilitation measures to the ecological integrity of rivers like the River Pielach where morphological conditions are good, whereas remaining channelization still limits the success of connectivity measures in the River Melk. Trap catch data were found to represent an essential source of additional information to assess the efficiency of connectivity measures shortly after their implementation. The negative correlations of the magnitude of the effect of different indices and metrics with the distance of assessment sites from river mouths obviously underline the importance of the river Danube as a source for the re-colonization process. While the indices tested were found to have limited ability to reflect short-term response of fish assemblages to continuum rehabilitation, guild metrics were able to detect improvements of the ecological status shortly after the implementation of connectivity measures. Six metrics showed significant differences between pre and post-project data reflecting the expected increase of the ecological integrity: (1) Fish Region Index (FRI; FIA, MULFA), (2) number of subdominant species and (3) number of flow-guilds (FIA), (4) number of type specific species (MULFA), (5) number of benthic species and (6) number of potamodromous species (EFI); the FRI differences were only significant when trap catch data were added. The EFI indicated a decline of ecological integrity through increases in the density of omnivorous species and the relative number of tolerant species as well as a decrease in the relative number of intolerant species. Significantly decreasing responses with the distance from the river mouth were documented by the EFI and MULFA-index, the FRI (FIA, MULFA), total biomass and for the number of type specific species (MULFA). Guest editors: R. L. Welcomme & G. Marmulla Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries     

Seasonality and controls of phytoplankton productivity in the middle Cape Fear River, USA

Our 1 year study was aimed at assessing seasonal patterns and controls on phytoplankton primary production (PPR) and biomass (chlorophyll a) in a fourth order section of the middle Cape Fear River in North Carolina, USA, and to determine the impact of three low-head lock and dam (LD) structures on these variables within the 70 km study reach of this coastal river. Mean concentrations of NO₃ ⁻–N, NH₄ ⁺–N and soluble reactive phosphorus (SRP) averaged 52.9, 6.0, and 3.6 μmol l⁻¹ in monthly sampling, while the average light attenuation coefficient was 2.4 m⁻¹. The average euphotic depth was 2.1 m. Nutrient concentrations and attenuation coefficients were not significantly different above versus below each LD, or along the entire study reach. Significantly higher concentrations of dissolved O₂ below versus above each LD were attributed to re-aeration during spillway transit. No seasonal pattern in physicochemical properties was apparent. Phytoplankton chlorophyll a concentrations ranged from <1 to 36 μg l⁻¹, while rates of primary production ranged from 18 to 2,580 mg C m⁻² day⁻¹, with values for both variables peaking in the spring and early summer. Chlorophyll a and primary productivity values were consistently higher above versus below each LD in May and June suggesting a seasonal effect, but values were otherwise similar such that overall means were not significantly different. Several factors point to light as the primary control on phytoplankton in the middle Cape Fear River: high nutrient concentrations; a low ratio of euphotic : mixing depth (0.46); progressive increases in chlorophyll a and radiocarbon uptake in all treatments in quarterly nutrient enrichment bioassays conducted at levels of irradiance elevated relative to in situ river values; and consistently low quarterly values of (maximum rate of chlorophyll-normalized C uptake; ≤3.7 mg C mg chl a⁻¹ h⁻¹) and I _k (light saturation parameter; ≤104 μmol photons m⁻² s⁻¹) for photosynthetic light–response (P–I) curves. Handling editor: L. Naselli-Flores     

Greenhouse gas fluxes from the eutrophic Temmesjoki River and its Estuary in the Liminganlahti Bay (the Baltic Sea)

We studied concentrations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) in the eutrophic Temmesjoki River and Estuary in the Liminganlahti Bay in 2003–2004 and evaluated the atmospheric fluxes of the gases based on measured concentrations, wind speeds and water current velocities. The Temmesjoki River was a source of CO₂, CH₄ and N₂O to the atmosphere, whereas the Liminganlahti Bay was a minor source of CH₄ and a minor source or a sink of CO₂ and N₂O. The results show that the fluxes of greenhouse gases in river ecosystems are highly related to the land use in its catchment areas. The most upstream river site, surrounded by forests and drained peatlands, released significant amounts of CO₂ and CH₄, with average fluxes of 5,400 mg CO₂–C m⁻² d⁻¹ and 66 mg CH₄–C m⁻² d⁻¹, and concentrations of 210 μM and 345 nM, respectively, but N₂O concentrations, at an average of 17 nM, were close to the atmospheric equilibrium concentration. The downstream river sites surrounded by agricultural soils released significant amounts of N₂O (with an average emission of 650 μg N₂O–N m⁻² d⁻¹ and concentration of 22 nM), whereas the CO₂ and CH₄ concentrations were low compared to the upstream site (55 μM and 350 nM). In boreal regions, rivers are partly ice-covered in wintertime (approximately 5 months). A large part of the gases, i.e. 58% of CO₂, 55% of CH₄ and 36% of N₂O emissions, were found to be released during wintertime from unfrozen parts of the river.     

丹江口北泰山庙旧石器遗址发掘简报

北泰山庙遗址位于汉水右岸第三级基座阶地。2006年11月—2007年1月对该遗址进行抢救性发掘, 揭露面积800m2, 出土石制品277件, 包括石核、石片、断块和石器。石器以大型为主, 砍砸器和刮削器为主要类型; 多采用锤击法加工石器。石制品面貌具有中国南方旧石器主工业的特点。根据地貌、地层和文化面貌对比, 推断遗址形成于中更新世早期。