Mathematical models and empirical studies have revealed two potentially disruptive influences on ecosystems; (1) instabilities caused by nonlinear feedbacks and time-lags in the interactions ofbiological species, and (2) stochastic forcings by a fluctuating environment. Because both of these phenomena can severely affect system survival, ecologists are confronted with the question of why complex ecosystems do, in fact, exist. Our study analyzes the basic themes of this research and identifies five general hypotheses that, in recent years, theoretical ecologists have built into models to increase their stability against disruptive feedback and stochasticity. To counter feedback instabilities, theoreticians have considered (1) functional interactions between species that act as stabilizers, (2) disturbance patterns that interrupt adverse feedback effects, and (3) the stabilizing effect of integrating small-spatial-scale systems into large landscapes. To decrease the influence of stochasticity, modelers have hypothesized (4) compensatory mechanisms operating at low population densities, and (5) the moderating effect of spatial extent and heterogeneity. We show that modeling based on these ideas can be organized in a systematic way. We also show that the stable equilibrium state should not be viewed as a fundamental property of ecological systems, but as a property that can emerge asymptotically from extrapolation to sufficiently large spatial scales.

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This study compares specific- and generic-level analyses of chironomid presence/absence data along a heavy-metal gradient. Eighteen binary similarity coefficients were calculated for five sampling stations from a small Ohio stream that receives an effluent containing zinc, copper, and chromium from a metal-plating industry. In general, the specific- and generic-level values were highly correlated and showed similar patterns across the 10 station comparisons. The basis for this correlation was then investigated by an assessment of both the amount (average number of species per genus) and the pattern (species to genus ratio trend) of information loss along the pollution gradient. Trends in the species to genus ratio along the gradient are viewed as indicative of the similarity of congenerics in their response to the gradient. The lack of a significant trend in the species to genus ratio in our data indicates that the agreement between specific- and generic-level analyses was due to the ability of a robust species distribution pattern to withstand a limited amount of random information loss, rather than any inherent similarity among congenerics reflected in their species to genus ratio trends. Analyses based on only a few species (e.g. abundant or indicator species) cannot afford as much information loss and must rely more heavily on similarity of congeneric species.

<p>Drinking water security in the UK is facing increasing pressure from rising demand, fuelled by population growth and rising periods of drought. Monitoring and regulation of water quality and related internal biogeochemical processes within drinking-water reservoirs is therefore paramount to maintaining security of supply, as well as allowing continued efficient and cost-effective management. In aquatic systems, internal biogeochemical processes are controlled by a complex set of oxygen-controlled forcing mechanisms; as diffuse pollution inputs from upstream catchments enter oxygen-dynamic reservoirs that frequently include nutrient- and metal-rich sediment, deleterious soluble chemical species (e.g., trace metals such as manganese, Mn) can be released from the sediment to the overlying water. Mn in particular is a problem for drinking water treatment plants. In light of oxygen-related water quality issues, almost all UK drinking water utilities use aeration systems to optimise oxygen concentrations and corresponding water quality and ecosystem health. </p><p>Blagdon Lake in Somerset, SW England is one such medium-size (1.8km2), shallow depth (max: 13.1m) drinking-water reservoir underlain by Mn-rich sediments. The goal of this project was to investigate the dynamics of Mn release into the overlying water, by coupling a catchment model (SWAT) and a reservoir model (CE-QUAL-W2) together. The coupled whole-system model would be assessed using multiple atmospheric, land-use, and catchment management scenarios to discern the driving processes of Mn release and quantify risk to future water security.</p><p>An extensive five-month field campaign was undertaken in Summer 2019 to build water quality time series and calibration datasets for the reservoir model (CE-QUAL-W2). Techniques and equipment deployed during the field work included: water sample filtration & soluble/insoluble Mn analysis at 2m depth intervals; permanently installed thermistor chains using Onset TidbiT v2 loggers at 1m depth resolution; water quality profiles from an EXO3 Sonde, logging pH, chlorophyll-α, conductivity, and turbidity; and surface sediment core Mn analysis. This data was then collated with atmospheric data (ERA5), and existing datasets of nutrient concentration data at multiple inflows (inc. NO2/NO3, Ammonium, Total P/Ortho P). Initial analysis of the data collected during the field campaign suggest that periods of stratification align with elevated Mn concentrations in the water column, directly relating soluble Mn release to air temperature.</p>

<p>Thermal destratification of lakes and reservoirs is a primary control on dissolved-oxygen levels below the thermocline. In such waterbodies, internal biogeochemical processes are often controlled by a complex set of oxygen-controlled forcing mechanisms. Therefore, preventing stratification by artificial processes has long been an important tool in maintaining dissolved oxygen concentrations and corresponding water quality and ecosystem health in drinking water reservoirs. Blagdon Lake in Somerset, SW England is a medium-size (1.8km<sup>2</sup>), shallow depth (max: 13.1m) drinking water reservoir. An extensive 6-month field campaign was undertaken in the summer of 2019 at the reservoir, measuring depth profiles of dissolved oxygen, turbidity, conductivity, temperature and pH using an EXO3 multiparameter sonde and a CastAway® CTD. In addition, two thermistor chains were permanently installed measuring temperature and dissolved oxygen concentrations using Onset TidbiT v2 loggers (1m depth intervals) through the water column at 30-minute temporal resolution and a miniDOT oxygen logger at the sediment-water interface respectively. These thermistor chains collected data from summer 2019 – autumn 2020. The data from this field campaign were analysed to investigate the effectiveness of the installed bubble-plume destratification system present at Blagdon Lake, SW England. Similar systems are used in 66% of UK reservoirs employing artificial mixing infrastructure, though very little has been published evaluating their effectiveness in such temperate, shallow, drinking water reservoirs. Initial analysis of the results indicates that the bubble-plume system, nor wind shear is effectively preventing spring/summer destratification for long periods, and that neither are the main factor controlling thermal stratification in Blagdon Lake. The data provides a unique opportunity to directly assess the impact of bubble-plume aerators and their effectiveness at thermal destratification to control dissolved oxygen and water quality in temperate, shallow water bodies.</p>