Ecosystems

The use of ground sampled water quality information for global studies is limited due to practicaland financial constraints. Remote sensing is a valuable means to overcome such limitations and to providesynoptic views of ambient water quality at appropriate spatio-temporal scales. In past years several large dataprocessing efforts were initiated to provide corresponding data sources. The Diversity II water quality datasetconsists of several monthly, yearly and 9-year averaged water quality parameters for 340 lakes worldwide andis based on data from the full ENVISAT MERIS operation period (2002–2012). Existing retrieval methods anddatasets were selected after an extensive algorithm intercomparison exercise. Chlorophyll-a, total suspendedmatter, turbidity, coloured dissolved organic matter, lake surface water temperature, cyanobacteria and floatingvegetation maps, as well as several auxiliary data layers, provide a generically specified database that can beused for assessing a variety of locally relevant ecosystem properties and environmental problems. For validationand accuracy assessment, we provide matchup comparisons for 24 lakes and a group of reservoirs representinga wide range of bio-optical conditions. Matchup comparisons for chlorophyll-a concentrations indicate meanabsolute errors and bias in the order of median concentrations for individual lakes, while total suspended matterand turbidity retrieval achieve significantly better performance metrics across several lake-specific datasets. Wedemonstrate the use of the products by illustrating and discussing remotely sensed evidence of lake-specificprocesses and prominent regime shifts documented in the literature. The Diversity II data are available fromdoi.pangaea.de/10.1594/PANGAEA.871462, and Python scripts for their analysis and visualization areprovided at github.com/odermatt/diversity/.

We present a new potentiometric sensor principle and a calibration protocol for in situ profiling of dissolved CO₂ with high temporal and spatial resolution in fresh water lakes. The sensor system is based on the measurement of EMF between two solid-contact ion selective electrodes (SC-ISEs), a hydrogen ion selective and a carbonate selective sensor. Since it relies on SC-ISEs, it is insensitive to changes in pressure, thus suitable for in situ studies. Also, as it offers a response time (t_95%) of <10 s, it allows for profiling applications at high spatial resolution. The proposed optimum in situ protocol accounts for the continuous drift and change in offset that remains a challenge during profiling in natural waters. The fast response resolves features that are usually missed by standard methods like the classical Severinghaus CO₂ probe. In addition, the insensitivity of the presented setup to dissolved sulfide allows also for measurements in anoxic zones of eutrophic systems. Highly resolved CO₂ concentration profiles obtained by the novel and robust SC-ISE setup along with the developed optimum in situ protocol allow investigating hotspots of biogeochemical processes, such as mineralization and primary production in the water column and help improving estimates for CO₂ turnover in freshwater systems.

Internal concentrations link external exposure to the potential effect, as they reflect what the organisms actually take up and experience physiologically. In this study, we investigated whether frequently detected risk-driving substances in water were found in the exposed organisms and if they are classified the same based on the whole body internal concentrations. Field gammarids were collected upstream and downstream of ten wastewater treatment plants in mixed land use catchments. The sampling was conducted in autumn and winter, during low flow conditions when diffuse agricultural input was reduced. The field study was complemented with laboratory and flume experiments to determine the bioaccumulation potentials of selected substances. For 32 substances, apparent bioaccumulation factors in gammarids were determined for the first time. With a sensitive multiresidue method based on online-solid phase extraction followed by liquid chromatography coupled to high resolution mass spectrometry, we detected 63 (semi-) polar organic substances in the field gammarids, showing higher concentrations downstream than upstream. Interestingly, neonicotinoids, which are particularly toxic toward invertebrates, were frequently detected and were further determined as major contributors to the toxic pressure based on the toxic unit approach integrating internal concentration and toxic potency. The total toxic pressure based on internal concentrations was substantially higher compared to when external concentrations were used. Thus, internal concentrations may add more value to the current environmental risk assessment that is typically based solely on external exposure.

Fertilization, crop uptake followed by plant harvest, runoff and erosion, and transformations ofphosphorus (P) in soil are the major factors influencing the P balance of croplands. It is important to integrateplant-soil-management interactions into consistent modeling systems to determine the effect of Pfertilization conditions on yields and to quantify P losses. Previous assessment of P losses on large scales didnot consider the interactions among these factors. Here we applied a grid-based crop model to estimateglobal P losses from three most produced crops: maize, rice, and wheat. The model was forced by detailed Pinput data sets over the period 1998–2002. According to our simulations, global P losses from the threecrops reached 1.2 Tg P/year, and about 44% of it was due to soil erosion. The global total P losses weredominated by contributions from a few hot spot regions. Reducing P fertilizer in regions experiencingexcessive P uses and hence losses, especially in China and India, could achieve the same yields as today andsave about two thirds of global total P inputs, with the cobenefits of declining global total P losses by 41%and downstream water quality improvement. Reducing soil erosion and retaining more crop residues oncroplands could further save P inputs and alleviate P losses. This study is of significance to determine themajor factors influencing P balance across regions of the world and help policy makers to propose efficientstrategies for tackling P-driven environmental problems.