A simple model of the eco-hydrodynamics of the epilimnion of Lake Tanganyika

1. The ecosystem response of Lake Tanganyika was studied using a four-component, nutrient–phytoplankton–zooplankton–detritus, phosphorus-based ecosystem model coupled to a nonlinear, reduced-gravity, circulation model. The ecosystem model, an improved version of the earlier eco-hydrodynamics model developed for Lake Tanganyika, was used to estimate the annual primary production of Lake Tanganyika and its spatial and temporal variability. The simulations were driven with the National Centres for Environmental Protection (NCEP) records for winds and solar radiation forcing.
2. The simulated annual cycles of the four ecosystem variables and the daily net primary production were compared with the observations. The comparison showed that simulations reproduced realistically the general features of the annual cycles of epilimnial phosphate, net primary production and plankton dynamics.
3. The climatic simulations for the years 1970–2006 yielded a daily averaged integrated upper layer net production ranging from 0.11 to 1.78 g C m⁻² day⁻¹ and daily averaged chlorophyll- a (chl- a ) from 0.16 to 4.3 mg m⁻³. Although the nutrient concentrations in the epilimnion during the strong wind years were high, the net production was low, which is partly because of the greater vertical mixing, produced by strong winds, exposing the phytoplankton to low light conditions in deeper waters. The simulated annual net production and chl- a agreed quite well with observed production available in the literature.
4. We envisage using this model to predict the future scenarios of primary productivity in the lake.     

Is speciation of demersal fishes in Lake Tanganyika restrained by physical limnological conditions?

Both Lake Malawi and Lake Victoria have many species of offshore demersal cichlids, most of which are stenotopic. In Lake Tanganyika there are fewer, more eurytopic, demersal species. These differences may be the effect of the physical regimes of the lakes. In Lake Victoria there is no permanent anoxic layer. In both the other lakes, water below 250 m depth is permanently anoxic and the seasonal cycle is dominated by upwelling. In Lake Malawi this is mainly derived from intermediate water containing free oxygen. In Lake Tanganyika upwelling involves hypolimnetic water, which may rise to within 80 m of the surface, causing great short-term changes in oxygen concentration over the depth range 50–250 m. This has inhibited the development of deep water species restricted to narrow depth ranges.     

Century-Long Warming Trends in the Upper Water Column of Lake Tanganyika

Lake Tanganyika, the deepest and most voluminous lake in Africa, has warmed over the last century in response to climate change. Separate analyses of surface warming rates estimated from in situ instruments, satellites, and a paleolimnological temperature proxy (TEX₈₆) disagree, leaving uncertainty about the thermal sensitivity of Lake Tanganyika to climate change. Here, we use a comprehensive database of in situ temperature data from the top 100 meters of the water column that span the lake’s seasonal range and lateral extent to demonstrate that long-term temperature trends in Lake Tanganyika depend strongly on depth, season, and latitude. The observed spatiotemporal variation in surface warming rates accounts for small differences between warming rate estimates from in situ instruments and satellite data. However, after accounting for spatiotemporal variation in temperature and warming rates, the TEX₈₆ paleolimnological proxy yields lower surface temperatures (1.46 °C lower on average) and faster warming rates (by a factor of three) than in situ measurements. Based on the ecology of Thaumarchaeota (the microbes whose biomolecules are involved with generating the TEX₈₆ proxy), we offer a reinterpretation of the TEX₈₆ data from Lake Tanganyika as the temperature of the low-oxygen zone, rather than of the lake surface temperature as has been suggested previously. Our analyses provide a thorough accounting of spatiotemporal variation in warming rates, offering strong evidence that thermal and ecological shifts observed in this massive tropical lake over the last century are robust and in step with global climate change.     

Influence of long-distance climate teleconnection on seasonality of water temperature in the world's largest lake--Lake Baikal, Siberia

Large-scale climate change is superimposed on interacting patterns of climate variability that fluctuate on numerous temporal and spatial scales--elements of which, such as seasonal timing, may have important impacts on local and regional ecosystem forcing. Lake Baikal in Siberia is not only the world's largest and most biologically diverse lake, but it has exceptionally strong seasonal structure in ecosystem dynamics that may be dramatically affected by fluctuations in seasonal timing. We applied time-frequency analysis to a near-continuous, 58-year record of water temperature from Lake Baikal to examine how seasonality in the lake has fluctuated over the past half century and to infer underlying mechanisms. On decadal scales, the timing of seasonal onset strongly corresponds with deviation in the zonal wind intensity as described by length of day (LOD); on shorter scales, these temperature patterns shift in concert with the El Nino-Southern Oscillation (ENSO). Importantly, the connection between ENSO and Lake Baikal is gated by the cool and warm periods of the Pacific Decadal Oscillation (PDO). Large-scale climatic phenomena affecting Siberia are apparent in Lake Baikal surface water temperature data, dynamics resulting from jet stream and storm track variability in central Asia and across the Northern Hemisphere.     

敦煌莫高窟干旱地区水分凝聚机理分析

通过对敦煌莫高窟戈壁地质结构的调查和洞窟检测,结合气象资料对戈壁土壤水分凝聚机理进行了分析,并根据形成机理在野外进行了水分凝结的覆膜实验.结果表明,在莫高窟戈壁区的上层砾砂中,由于强烈的温度日较差变化,形成了凝结水分;另外源于地下深处的水分通过土壤盐分的吸湿吸附作用在地下10～40cm范围内相对富集,并由于剧烈的波动呈现时空异质性变化.将凝结、吸湿吸附等方式形成的土壤水分统称为凝聚水分.凝聚是水分存储于一定土壤的结构过程,与太阳辐射、温度、湿度等气候因子密切相关.变温层土壤的温度、盐分、湿度、结构、密闭程度、地热等对水分的凝聚有重要影响.水分的凝聚机理对干旱地区的生态建设和文物保护具有重要的现实意义.     

Calculating solar and longwave radiation for a Mediterranean lake under various weather conditions

Two years of hourly measurements of global solar radiation and downward longwave radiation were used to estimate the radiative balance of Lake Banyoles, a small karstic Mediterranean lake. The performance of several empirical estimation equations on an hourly and a daily basis were evaluated taking into account various meteorological conditions. The new coefficients in the formulae for the effective emittance, which have been derived from meteorological data, demonstrate that these coefficients strongly depend on the radiation climate of the respective area. In the Mediterranean climate of Lake Banyoles, changes in wind direction and relative humidity after the vertical distribution of vapour pressure beneath the cloud layer. Different median experimental errors were found depending on the time scale and cloud cover. Comparison of global solar radiation measured at Banyoles with estimated values shows good agreement for clear skies, especially for daily means. On a daily scale, the root mean squared (r.m.s.) error was found to be 8% for solar radiation and 12% for longwave radiation. On an hourly scale, different r.m.s. errors were obtained depending on the degree of cloud cover.     

A generalized,lumped-parameter model of photosynthesis,evapotranspiration and net primary production in temperate and boreal forest ecosystems

Summary PnET is a simple, lumped-parameter, monthlytime-step model of carbon and water balances of forests built on two principal relationships: 1) maximum photosynthetic rate is a function of foliar nitrogen concentration, and 2) stomatal conductance is a function of realized photosynthetic rate. Monthyly leaf area display and carbon and water balances are predicted by combining these with standard equations describing light attenuation in canopies and photosynthetic response to diminishing radiation intensity, along with effects of soil water stress and vapor pressure deficit (VPD). PnET has been validated against field data from 10 well-studied temperate and boreal forest ecosystems, supporting our central hypothesis that aggregation of climatic data to the monthly scale and biological data such as foliar characteristics to the ecosystem level does not cause a significant loss of information relative to long-term, mean ecosystem responses. Sensitivity analyses reveal a diversity of responses among systems to identical alterations in climatic drivers. This suggests that great care should be used in developing generalizations as to how forests will respond to a changing climate. Also critical is the degree to which the temperature responses of photosynthesis and respiration might acclimate to changes in mean temperatures at decadal time scales. An extreme climate change simulation (+3° C maximum temperature, –25% precipitation with no change in minimum temperature or radiation, direct effects of increased atmospheric CO₂ ignored) suggests that major increases in water stress, and reductions in biomass production (net carbon gain) and water yield would follow such a change.     

<Emphasis Type="Italic">Limnocnida tanganyicae</Emphasis> medusae (Cnidaria: Hydrozoa): a semiautonomous microcosm in the food web of Lake Tanganyika

Medusae are important members of marine food webs, but are rare in lakes. In one of the largest lakes in the world, Lake Tanganyika, a small medusa (Limnocnida tanganyicae) is a prominent component of zooplankton. We used field and laboratory methods to study the ecological role of Lake Tanganyika medusae, which occasionally reached high local densities in the whole epilimnion. The largest individuals showed low amplitude, diel vertical migration which minimized their exposure to harmful UV radiation and also may be important for picocyanobacteria regularly present in the medusae. The endosymbiotic picocyanobacteria differed morphologically among medusae and were predominantly one Lake Biwa type Cyanobium sp. that typically was abundant in the water column. Under light, some medusae were net primary producers. Although nitrogen stable isotopic ratios indicated that the free-living cyanobacteria were nitrogen-fixers, the picocyanobacteria in medusae obtained nitrogen predominantly from their host. Stable isotopic ratios of carbon and nitrogen further suggested that copepods were the most likely prey for the medusae. Lake Tanganyika medusae apparently base their metabolism both on animal and plant sources, with possible internal cycling of nutrients; however, the role of picocyanobacteria gardening in the Lake Tanganyika ecosystem and its medusae requires quantification.     

Implications of climate change for Daphnia in alpine lakes: predictions from long-term dynamics, spatial distribution, and a short-term experiment

Alpine lakes may be particularly useful as sentinels of climate change because they are highly sensitive to environmental conditions. To explore the potential biotic consequences of climate change in these systems, we conducted paleo- and neoecological observational studies, as well as a short-term experiment to examine Daphnia responses to changing environmental conditions in Rocky Mountain alpine lakes. Our analysis of a sediment core from Emerald Lake representing two periods from the Holocene revealed a significant positive relationship between the abundance of Daphnia remains and fossil Aulacoseira lirata, a diatom associated with deeper mixing depths. In addition, we detected a significant increase in mean Daphnia density in the long-term record (1991–2005) from Pipit Lake, a trend that correlated well with increases in mean surface temperature. In our survey of Daphnia in 10 lakes in the Canadian Rocky Mountains, Daphnia abundance was positively correlated with both dissolved organic carbon concentration and temperature. Finally, our short-term incubation experiment demonstrated significant effects of physical conditions (i.e., temperature and/or UV radiation) and water chemistry on the juvenile growth rate of Daphnia. Overall, our findings highlight the sensitivity of Daphnia to changes in mixing depth, water temperature, and dissolved organic matter, three limnological variables that are highly sensitive to changes not only in air temperature, but also to precipitation and location of the treeline in alpine catchments. Thus, we conclude that Daphnia abundance could serve as a powerful sentinel response to climate change in alpine lakes of the Rocky Mountains.     

MicroclimOz – A microclimate data set for Australia,with example applications

Many problems in pure and applied ecology require the quantification of above‐ and below‐ground microclimates. Here I describe a data set of hourly microclimates for the Australian continent, simulated from the years 1990 to 2017 across a grid of 1893 locations approx. 60 km apart. The data were generated with the NicheMapR microclimate model, driven by 0.05° gridded daily meteorological forcing data (air temperature, wind speed, humidity, cloud cover, rainfall), 0.025° elevation and 0.008° soil texture data. The above‐ground microclimate variables include horizontal plane solar radiation, solar zenith angle, sky temperature (from which down‐welling longwave radiation can be computed), air temperature, relative humidity and wind speed at 1 and 120 cm height, and snow depth. The below‐ground variables include soil temperature, pore humidity, soil moisture and soil water potential for 0, 2.5, 5, 10, 15, 20, 30, 50, 100 and 200 cm below‐ground. The computations are for four shade levels (0%, 50%, 70% and 90%). The data set can be used for a wide variety of applications, including the computation of heat and water budgets of organisms, the potential for vegetation growth, and the computation of stress and growth indices. The use of daily forcing data also allows assessments of the consequences of extreme events including heat waves. Example applications are provided for computing plant growth potential, grasshopper egg development, lizard body temperature and mammalian energy and water requirements.     

东北城市露水凝结观测及其与常规气象要素的关系

露水是城市生态系统水循环组成部分,是重要的凝结水资源和湿度来源,为了揭示"全球变暖"对我国东北地区城市露水凝结的影响,于2014和2015年植物生长季对长春市绿地区、道路区及裸土区露水强度和气象因子进行监测和相关性分析。结果表明,东北城市绿地区露水强度与相对湿度、露点温度、气温、风寒温度、太阳辐射(n=254,P0.01)正相关,与PM_(2.5)、PM_(10)、空气质量指数、夜间风速、大气压(n=254,P0.01)负相关。东北城市年露日数为132—136d,占无霜期的62.5%左右。绿地区是城市生态系统水汽凝结的主要区域,绿地区占市区面积的比例是城市年露水量的决定因子,长春市年露水凝结量约为23—35mm,如城市绿地区所占比例降低至5%,年露水量基本可忽略不计。东北城市露水强度可通过I=(-5.9+0.156RH-0.86V_(night)+0.117R_n)×10~(-2)(R~2=0.857)模型进行模拟。结合研究区1965—2015年植物生长期夜间凝露段气候因子的变化趋势,判断东北城市生态系统露水量的变化率为-1.07mm/10a(P0.01)。在相对湿度、夜间风速和太阳辐射共同影响条件下,研究区气候变化对露水凝结影响不大。提供了城市不同下垫面露水监测及计算的方法,完善了不同生态系统露水监测体系,通过间接模型法构建了露水强度模拟模型,进一步明确了气候变化对近地表水循环的影响。     

Impact of climate variability on the hydrology of the Sudd wetland: signals derived from long term (1900–2000) water balance computations

The Sudd wetland is a huge swampy area (30,000–40,000 km²), with vegetation composed mainly of papyrus, water hyacinth and grasslands. It is located in South Sudan, and is of vital importance for livelihoods, ecosystem services and water resources. Half of the White Nile flow evaporates when passing through the Sudd (~16,000 10⁶ m³/year). Historically, this phenomenon triggered several water conservation projects in the Nile region (the Jonglei Canal Project). However, the available information on the hydrology of the Sudd is very limited, and mostly outdated. This paper investigates the long term dynamics of the Sudd hydroclimatology (water balance components), and how it affects the wetland areal extent. The water balance results show that the extent of the Sudd wetland area is determined both by the regional climate (outflow from Lake Victoria) and the local climate, represented by precipitation and evaporation over the wetland itself. The long term trends of the Sudd hydrology from 1900 to 2000 have been analyzed with the Mann–Kendall test statistics. The water flows into and out of the Sudd demonstrate a statistically significant increasing trends during the last 100 years. This can be attributed to increasing rainfall over Lake Victoria in the early 1960s. The daily maximum and minimum temperature in the Sudd shows an increasing trend of 0.6 and 1.5 °C, respectively, over the last 100 years. However, this has not caused any change of the wetland actual evaporation (open water evaporation plus plant transpiration). The impact of the temperature rise has likely been compensated by a reduction of the relative humidity and solar radiation over the wetland. The statistical test shows that both relative humidity and solar radiation (sunshine hours) has significantly decreased, each reduced by 10 % over the last 50 year. The precipitation over the Sudd showed no significant change during the last 100 years. On the other hand, the areal extent of the Sudd wetland increased by 19,000 km² (80 %) during the last 100 years, as a result of the increased inflows. The long term variability of the Sudd areal extent provides new results and deeper insights of the two-way land surface climate feedbacks, and informs wetland conservation and water resources management for this important tropical wetland.     

人工输水对石羊河下游青土湖区域生态环境的影响分析

通过对石羊河下游青土湖人工输水后水面形成区环境要素变化的调查研究,分析了水面形成对区域地下水位、植被、大气温湿度、风速等的影响。结果表明:(1)由于输水方式、输水时间集中等因素影响,区域水面形成快速;且每个输水周期完成6个月后的区域保留水面积持续增大,4a间水面积增加4.52倍,面积扩大的叠加效应明显。(2)输水作用和水面的形成,促使输水区域地下水埋深由6m,提升到0.6—3.2m。(3)水面形成促进了区域以白刺为代表的单一荒漠植被群落向芦苇草甸、盐化草甸等多样化群落演替。(4)水面形成的"冷岛效应"明显,促进了区域小气候环境的改善;输水区500m范围平均温度降低55.67%,湿度增加3倍。人工输水对青土湖区域生态环境的改善产生了明显的积极作用,但输水政策的持续性、输水策略调整等不确定性影响,以及水面形成对局部范围风沙活动、植物物种多样性等方面的负面影响值得关注和深入研究。     

Influence of Soil Physical Properties on Plants of the Mussununga Ecosystem, Brazil

Distribution ranges of plant species are related to physical variables of ecosystems that limit plant growth. Therefore, each plant species response to physical factors builds up the functional diversity of an ecosystem. The higher the species richness of an ecosystem, the larger the probability of maintaining functions and the higher the potential number of plant functional groups (FGs). Thus, the richness potentially increases the number of functions of the highly diverse Atlantic Rainforest domain in Brazil. Severe plant growth limitations caused by stress, however, decrease species richness. In the Spodosols of the Mussununga, an associated ecosystem of Atlantic Rainforest, the percentage of fine sand is directly related to water retention. Moreover, the depth of the cementation layer in the Mussununga??s sandy soil is a physical factor that can affect the plants?? stress gradients. When a shallow cementation layer depth is combined with low water retention in soils and with low fine sand percentage, the double stresses of flooding in the rainy season and water scarcity in the dry season result. This study aimed to identify FGs among Mussununga plant species responding to water stress gradients of soil and to verify the effects of the gradients on plant species richness of the Mussununga. A canonical correspondence analysis (CCA) of species abundance and soil texture variables was performed on 18 plots in six physiognomies of the Mussununga. Species richness rarefactions were calculated for each vegetation form to compare diversity. The two main axes of the CCA showed two FGs responding to soil texture and cementation layer depth: stress tolerator species and mesic species. Physical variables affect plant diversity, with species richness rising as the fine sand proportion also rises in the Mussununga. The effect of the cementation layer is not significantly related to species richness variation.     

Evolution de la temperature de l'oxygene dissous et de la transparence dans la baie Nord du lac Tanganika

Resume Nous décrivons dans ce travail l'évolution de la température de l'oxygène dissous et de la transparence dans le bassin N. du lac Tanganika.La température de l'eau ne subit des fluctuations intéressantes au cours de l'année que dans les 100 premiers mètres de la surface. Les eaux du Tanganika offrent une temperature élevée jusqu' à ses plus grandes profondeurs; à 1.400 m. la température de l'eau est encore de 23.35° C. La température des eaux superficielles dépend de l'insolation journalière et les variations saisonnières n'affectent qu'une épaisseur d'eau d'une centaine de mètres. La couche oxygénée de l'eau est très faible par rapport aux énormes profondeurs du lac. Dans le bassin N. elle varie au cours de l'année entre les extrêmes de 45 m. et de 115 m.; la plupart du temps la limite de l'oxygène dissous se situant à 75–80 m de profondeur.Les eaux superficielles sont fortement oxygénées, leur teneur en oxygène dissous oscille autour de 100% de satuation, jusqu'au thermocline elles sont encore oxygénées à 80–90%.Le thermocline est toujours plus haut que la limite de l'oxygène dissous et ne présente absolument pas une barrière biologique comme c'est le cas dans la plupart des lacs des régions tempérées.La transparence des eaux du lac Tanganika est considérable, elle atteint souvent 20 m; la moyenne au cours de l'année se situant aux environs de 15 m.

---

Summary The author describes the temperature, oxygen and transparency conditions in the Northern basin of Lake Tanganyika.The fluctuations in the temperature of the waters in the course of the year is of interest only down to a depth of 100 m.The temperature of water in Lake Tanganyika is high even in the greatest depths; at 1.400 m depth the temperature of the water is still 23.35° C. The temperature of surface water depends on the daily solar radiation. The influence of seasonal variations is felt only down to a depth of about one hundred meters.The oxygenated layer of water is very thin in comparison with the very great depth of the lake. In the northern basin, this layer varies in thickness between 45 and 115 m, the limit of dissolved oxygen being at a depth of about 75 m most of the time.The oxygen concentration in superficial waters is very high and nearly reaches the saturation point. Down to the thermoclinal point, the concentration is still 80–90 % The thermocline is always higher than the limit of dissolved oxygen, it does not at all constitute a biological barrier as it does in most lakes in temperate climates. The waters of Lake Tanganyika are very transparent, their transparency often reaches the depth of 20 m, the average for the year being 15 m.

---

---

Centre de Recherches du Tanganika (Uvira) Institut pour la Recherche Scientifique en Afrique Centrale I.R.S.A.C.     

Arctic mosses govern below-ground environment and ecosystem processes

Mosses dominate many northern ecosystems and their presence is integral to soil thermal and hydrological regimes which, in turn, dictate important ecological processes. Drivers, such as climate change and increasing herbivore pressure, affect the moss layer thus, assessment of the functional role of mosses in determining soil characteristics is essential. Field manipulations conducted in high arctic Spitsbergen (78° N), creating shallow (3 cm), intermediate (6 cm) and deep (12 cm) moss layers over the soil surface, had an immediate impact on soil temperature in terms of both average temperatures and amplitude of fluctuations. In soil under deep moss, temperature was substantially lower and organic layer thaw occurred 4 weeks later than in other treatment plots; the growing season for vascular plants was thereby reduced by 40%. Soil moisture was also reduced under deep moss, reflecting the influence of local heterogeneity in moss depth, over and above the landscape-scale topographic control of soil moisture. Data from field and laboratory experiments show that moss-mediated effects on the soil environment influenced microbial biomass and activity, resulting in warmer and wetter soil under thinner moss layers containing more plant-available nitrogen. In arctic ecosystems, which are limited by soil temperature, growing season length and nutrient availability, spatial and temporal variation in the depth of the moss layer has significant repercussions for ecosystem function. Evidence from our mesic tundra site shows that any disturbance causing reduction in the depth of the moss layer will alleviate temperature and moisture constraints and therefore profoundly influence a wide range of ecosystem processes, including nutrient cycling and energy transfer.     

Synergistic effects associated with climate change and the development of rocky shore molluscs

Global climate change and ozone layer thinning will simultaneously expose organisms to increasingly stressful conditions. Early life stages of marine organisms, particularly eggs and larvae, are considered most vulnerable to environmental extremes. Here, we exposed encapsulated embryos of three common rocky shore gastropods to simultaneous combinations of ecologically realistic levels of ultraviolet radiation (UVR), water temperature stress and salinity stress to identify potential interactions and associated impacts of climate change. We detected synergistic effects with increases in mortality and retardation in development associated with the most physiologically stressful conditions. The effects of UVR were particularly marked, with mortality increasing up to 12‐fold under stressful conditions. Importantly, the complex outcomes observed on applying multiple stressors could not have been predicted from examining environmental variables in isolation. Hence, we are probably dramatically underestimating the ecological impacts of climate change by failing to consider the complex interplay of combinations of environmental variables with organisms.     

Influences of ENSO and PDO phenomena on the local climate variability can drive extreme temperature and depth conditions in a Pampean shallow lake affecting fish communities

The aim of this study was to characterize occurrence of extreme temperature and depth conditions affecting fish community in a shallow lake as result of local climate variability, in turn influenced by the ENSO and PDO phenomena. Extreme depth and water temperature events (modeled from local weather conditions) were characterized from 1966 to 2012 to estimate changes in Chascomús lake fish communities. The ENSO and PDO influences on the occurrence probability of these ecosystem changes were investigated. Four significant changes in Chascomús Lake fish assemblage were identified during period assessed, as response to extreme temperature and depth events. Extreme high depth conditions would have changed fish community during 1987 and 2002, leading to a configuration characterized by the absence of the most emblematic fish species in Chascomús Lake, the pejerrey (Odontesthes bonariensis). On the other hand, extreme low water temperatures would have promoted a fish community characterized by the dominance of this last species during 1966–1986, 1997–2001 and 2008–2013 periods. Furthermore, extreme shortening in pejerrey spawning season was significantly related with decrease of its relative abundance. The occurrence probability of the extreme physical conditions modifying Chascomús Lake fish communities was significantly explained by ENSO (by depth influences) and by PDO (by water temperature influences). Thus, this study showed strong correlations between the ENSO and PDO influences and the occurrence probability of the extreme physical conditions changing fish community in Chascomús Lake.     

Effects of solar UV radiation on aquatic ecosystems and interactions with climate change.

Recent results continue to show the general consensus that ozone-related increases in UV-B radiation can negatively influence many aquatic species and aquatic ecosystems (e.g., lakes, rivers, marshes, oceans). Solar UV radiation penetrates to ecological significant depths in aquatic systems and can affect both marine and freshwater systems from major biomass producers (phytoplankton) to consumers (e.g., zooplankton, fish, etc.) higher in the food web. Many factors influence the depth of penetration of radiation into natural waters including dissolved organic compounds whose concentration and chemical composition are likely to be influenced by future climate and UV radiation variability. There is also considerable evidence that aquatic species utilize many mechanisms for photoprotection against excessive radiation. Often, these protective mechanisms pose conflicting selection pressures on species making UV radiation an additional stressor on the organism. It is at the ecosystem level where assessments of anthropogenic climate change and UV-related effects are interrelated and where much recent research has been directed. Several studies suggest that the influence of UV-B at the ecosystem level may be more pronounced on community and trophic level structure, and hence on subsequent biogeochemical cycles, than on biomass levels per se.     

Water stress and insect herbivory interactively reduce crop yield while the insect pollination benefit is conserved

Climate change is predicted to hamper crop production due to precipitation deficits and warmer temperatures inducing both water stress and increasing herbivory due to more abundant insect pests. Consequently, crop yields will be impacted simultaneously by abiotic and biotic stressors. Extensive yield losses due to such climate change stressors might, however, be mitigated by ecosystem services such as insect pollination. We examined the single and combined effects of water stress, insect herbivory and insect pollination on faba bean yield components and above‐ and belowground plant biomass under realistic field conditions. We used rainout shelters to simulate a scenario in line with climate change projections, with adequate water supply at sowing followed by a long period without precipitation. This induced a gradually increasing water stress, culminating around crop flowering and yield formation. We found that gradually increasing water stress combined with insect herbivory by aphids interactively shaped yield in faba beans. Individually, aphid herbivory reduced yield by 79% and water stress reduced yield by 52%. However, the combined effect of water stress and aphid herbivory reduced yield less (84%) than the sum of the individual stressor effects. In contrast, insect pollination increased yield by 68% independently of water availability and insect herbivory. Our results suggest that yield losses can be greatly reduced when both water stress and insect herbivory are reduced simultaneously. In contrast, reducing only one stressor has negligible benefits on yield as long as the crop is suffering from the other stressor. We call for further exploration of interactions among ecosystem services and biotic and abiotic stressors that simulate realistic conditions under climate change.