Helen M. Baulch

Modelling phosphorus dynamics in multi-branch river systems: a study of the Black River, Lake Simcoe, Ontario, Canada.

High rates of nutrient loading from agricultural and urban development have resulted in surface water eutrophication and groundwater contamination in regions of Ontario. In Lake Simcoe (Ontario, Canada), anthropogenic nutrient contributions have contributed to increased algal growth, low hypolimnetic oxygen concentrations, and impaired fish reproduction. An ambitious programme has been initiated to reduce phosphorus loads to the lake, aiming to achieve at least a 40% reduction in phosphorus loads by 2045. Achievement of this target necessitates effective remediation strategies, which will rely upon an improved understanding of controls on nutrient export from tributaries of Lake Simcoe as well as improved understanding of the importance of phosphorus cycling within the lake. In this paper, we describe a new model structure for the integrated dynamic and process-based model INCA-P, which allows fully-distributed applications, suited to branched river networks. We demonstrate application of this model to the Black River, a tributary of Lake Simcoe, and use INCA-P to simulate the fluxes of P entering the lake system, apportion phosphorus among different sources in the catchment, and explore future scenarios of land-use change and nutrient management to identify high priority sites for implementation of watershed best management practises.

Controls on greenhouse gas concentrations in polymictic headwater lakes in Ireland

Freshwater lakes are known to release carbon dioxide (CO(2)) and methane (CH(4)) to the atmosphere; however, the importance of lakes in global nitrous oxide (N(2)O) budgets is not yet known. Further, despite the abundance of small lakes on the landscape, neither emissions of these gases nor their drivers are well described. Dissolved concentrations of CO(2), CH(4) and N(2)O greenhouse gases were related to water chemistry, hydrology and catchment characteristics in order to identify factors controlling gas concentrations for 121 small Irish headwater lakes (median area: 2.0ha) in relatively undisturbed catchments; lake-atmosphere gas fluxes were also calculated. The majority of lakes were supersaturated (relative to the atmosphere) with CO(2) and N(2)O while CH(4) was above saturation in all lakes. Dissolved gas concentrations were correlated with land cover (rock, forest and grassland), deuterium excess (an indicator of hydrologic character) and lake organic carbon concentrations, although dissolved CO(2) exhibited few significant relationships. Principal components analysis indicated that higher levels of CH(4) and N(2)O supersaturation were exhibited under different conditions. Methane supersaturation was highest in low elevation catchments with an evaporative hydrologic character and high organic carbon concentrations. In contrast, lakes characteristic of N(2)O supersaturation were low in carbon and located in more rapidly flushed higher elevation catchments. Estimated fluxes of CO(2), CH(4) and N(2)O to the atmosphere averaged 14, 0.36 and 1.3×10(-3)mmolm(-2)d(-1), respectively.

Phosphorus dynamics across intensively monitored subcatchments in the Beaver River

Abstract We report results from a spatially intensive monitoring and modelling study to assess phosphorus (P) dynamics in the Beaver River, a tributary of Lake Simcoe, Ontario. We established multiple monitoring stations (9 flow and 24 water quality stations) from headwaters to near the outflow that were operated for 2 field seasons, complementing longer term data from a flow monitoring site and water chemistry monitoring site. We applied the Branched-INCA-P model, which allows fully distributed simulations supported by highly distributed monitoring data. Using spatially distributed data helped better understand variable P and sediment dynamics across the catchment and identify key model uncertainties and uncertainties related to catchment P management. Measured and modelled total P concentrations often exceeded provisional water quality thresholds in many areas of the catchment and highlight the value of studying water quality across multiple subcatchments rather than at a single site. Total P export coefficients differed widely among subcatchments, ranging from 2.1–21.4 kg km−2 y−1 over a single year. Export coefficients were most strongly (negatively) related to the proportion of wetland cover in subcatchments. The INCA-P model captured spatial variation in P concentrations relatively well, but short-term temporal variability in the observed data was not well simulated across sites, in part due to unmodelled hydrological phenomena including beaver activity and unknown drivers of P peaks that were not associated with hydrological events.

Who Smells? Forecasting Taste and Odor in a Drinking Water Reservoir.

Taste and odor problems can impede public trust in drinking water and impose major costs on water utilities. The ability to forecast taste and odor events in source waters, in advance, is shown for the first time in this paper. This could allow water utilities to adapt treatment, and where effective treatment is not available, consumers could be warned. A unique 24-year time series, from an important drinking water reservoir in Saskatchewan, Canada, is used to develop forecasting models of odor using chlorophyll a, turbidity, total phosphorus, temperature, and the following odor producing algae taxa: Anabaena spp., Aphanizemenon spp., Oscillatoria spp., Chlorophyta, Cyclotella spp., and Asterionella spp. We demonstrate, using linear regression and random forest models, that odor events can be forecast at 0-26 week time lags, and that the models are able to capture a significant increase in threshold odor number in the mid-1990 s. Models with a fortnight time-lag show a high predictive capacity (R(2) = 0.71 for random forest; 0.52 for linear regression). Predictive skill declines for time lags from 0 to 15 weeks, then increases again, to R(2) values of 0.61 (random forest) and 0.48 (linear regression) at a 26-week lag. The random forest model is also able to provide accurate forecasting of TON levels requiring treatment 12 weeks in advance-93% true positive rate with a 0% false positive rate. Results of the random forest model demonstrate that phytoplankton taxonomic data outperform chlorophyll a in terms of predictive importance.

Modelling phosphorus in Lake Simcoe and its subcatchments: scenario analysis to assess alternative management strategies

Abstract In Lake Simcoe (Ontario, Canada), anthropogenic phosphorus (P) loads have contributed to increased algal growth, low hypolimnetic dissolved oxygen concentrations, and impaired fish reproduction. Management targets to control eutrophication require an ambitious programme to reduce P loads to the lake. Remediation strategies rely upon an improved understanding of P sources and assessment of the effectiveness of different control options. Here we present an application of the integrated catchment model for phosphorus (INCA-P) to examine P sources across the Lake Simcoe watershed and simulate in-lake P concentrations. This is the first application of INCA-P to a complex watershed of this nature and the first to include a lake component. We evaluated a set of management actions to simulate anticipated effects of P reduction strategies on in-lake total phosphorus (TP) concentrations. The INCA-P scenarios show the difficulty of achieving large-scale reductions from the watershed, given the low rates of P export; however, the study shows that a multifaceted strategy, including fertilizer reduction, addition of buffer strips, more stringent controls on sewage treatment plant effluent, and reduced deposition of P to the lake surface, could achieve a 25% reduction in lake-water TP concentrations and produce TP close to the target of 0.01 mg L−1.

Isotopic Character of Nitrous Oxide Emitted from Streams

Global models have indicated agriculturally impacted rivers and streams may be important sources of the greenhouse gas nitrous oxide (N(2)O). However, there is significant uncertainty in N(2)O budgets. Isotopic characterization can be used to help constrain N(2)O budgets. We present the first published measurements of the isotopic character of N(2)O emitted from low (2-4) order streams. Isotopic character of N(2)O varied seasonally, among streams, and over diel periods. On an annual basis, δ(18)O of emitted N(2)O (+47.4 to +51.4‰; relative to VSMOW) was higher than previously reported for larger rivers, but δ(15)N of emitted N(2)O (-16.2 to +2.4‰ among streams; relative to atmospheric N(2)) was similar to that of past studies. On an annual basis, all streams emitted N(2)O with lower δ(15)N than tropospheric N(2)O. Given these streams have elevated nitrate concentrations which are associated with enhanced N(2)O fluxes, this supports the hypothesis that streams are contributing to the accumulation of (15)N-depleted N(2)O in the troposphere.

In the cold light of day: the potential importance of under-ice convective mixed layers to primary producers

Abstract Temperate lakes are ice covered for much of the year; however, winter lake conditions have not been well studied and are undergoing rapid change. Using data collected during ice-on periods from 4 north-temperate water bodies, we report observations of stable surface layers, solar-induced convective mixed layers, and their potential impacts on phytoplankton. The convective mixed layer is defined as the region where the convective Richardson number (Ri) is ≤1. In the absence of a convective mixed layer, peaks in chlorophyll a were near the ice–water interface. Light conditions here seemed sufficient to support phytoplankton biomass accrual in the short-term in 50% of our measurements, although snow depths >13.5 cm may lead to light limitation. When a convective mixed layer was present, light conditions were sufficient for biomass accrual in 37.5% of cases. The frictional timescale for damping averaged 15 minutes, indicative of a lack of mixing at night. Convective mixing depths and velocity increased as snow declined, and results demonstrated the potential for rapid convective mixed layer deepening (up to 6.6 m h−1), underscoring the highly dynamic physical environment under ice. Although declining periods of ice cover have been subject to much attention, changes in snow cover may have equally important implications for primary producers and the potential for under-ice blooms. This link between physics and biology must be further explored to better understand how changing winters will affect water bodies.

Asking the right questions about nutrient control in aquatic ecosystems.

E remains the greatest stressor affecting freshwater ecosystems across North America and Europe. However, over the past five years, the scientific literature has seen a resurrection of the debate over causes of eutrophication, with resulting confusion in management circles. This debate has been poorly defined, fractious, and oftentimes counterproductive. Eutrophication has been defined as the process leading to increased algal productivity in lakes through time. It can be a natural process, as lakes age; or, in the case of cultural eutrophication, it can be facilitated by anthropogenic nutrient inputs. Management concern about eutrophication centers on a change from a desirableoften clear water state, to an undesirable state, exemplified by issues of low hypolimnetic dissolved oxygen, nuisance algal productivity, and in many cases, production of algal toxins. Unfortunately, this may not be a linear change through time, but instead can occur as a state shift or regime change. More unfortunate, is that although eutrophication is reversible, it can take decades or centuries to induce a shift back from a degraded eutrophic state into a more natural, desirable condition. It is this state change and associated degradation of key ecosystem services that matters most to stakeholders and policy makers. Rarely are managers concerned about small, incremental changes in productivity that are of significant interest to science (Figure 1, arrow 1), yet these incremental changes, also correctly termed ‘eutrophication’ are where much the debate appears to derive. The question fundamental to eutrophication control is not “what is the limiting nutrient”, nor is it “can we induce a decrease in algal productivity”, but how can we prevent a state shift into an undesirable state, and how can we push an ecosystem back from a degraded state via nutrient control. If we subscribe to the assumption that a single nutrient is limiting to primary producers, then control of that nutrient will reduce productivity until productivity becomes limited by some other resource. So, where researchers argue that control of nitrogen (N) will reduce algal productivity, this is often correct in ecosystems like many agriculturally impacted prairie landscapes, where phosphorus (P) is replete. However, it remains to be seen whether N control could induce a shift to a desirable state. Although productivity may be controlled, changes may be small, incremental shifts of little interest to managers (e.g., Figure 1, arrow 3). Indeed, to date, it has not been clearly demonstrated that N addition in freshwaters can induce a change to a highly degraded state. More research on this topic is surely forthcoming, and will help clarify the role of N in eutrophication of inland lakes, and the potential importance of N control in remediating eutrophic systems. While the case for N in lake eutrophication, and N control in helping induce a shift back to desired conditions has yet to be made in lakes, the case for N control at a landscape or watershed scale is nuanced, but stronger. Our understanding of responses of rivers to different nutrients is even poorer than our ability to understand responses of divergent lake types. Variable light and flow regimes, temperatures, sediment composition, and nutrient delivery make streams and rivers a more complex mosaic of shifting limitation and variable drivers of eutrophication. As in lakes, there is no question that N affects the algal community, and other aspects of the ecosystem, and the effects of N are likely to vary with N species (nitrate, ammonia, or organic N). Nutrient limitation bioassays (admittedly not at the spatial or temporal scale necessary to fully understand the role

Can algal uptake stop NO3- pollution?

Arising from Cardinale, B. J. 472, 86–89 (2011)10.1038/nature09904The influence of biodiversity on ecosystem function has been of interest to community ecologists for decades. Recently, Cardinale reported that biodiversity affects nitrate (NO3−) uptake in algal communities and that, as a result, biodiversity may help mitigate nutrient pollution. Although Cardinale’s conclusions about niche partitioning are interesting (figure 2 in ref. 1), his extension of these findings to problems of nutrient pollution is premature. Algal uptake is only a short-term nitrogen sink; control of NO3− pollution requires long-term solutions.

Citizen science shows systematic changes in the temperature difference between air and inland waters with global warming

Citizen science projects have a long history in ecological studies. The research usefulness of such projects is dependent on applying simple and standardized methods. Here, we conducted a citizen science project that involved more than 3500 Swedish high school students to examine the temperature difference between surface water and the overlying air (Tw-Ta) as a proxy for sensible heat flux (QH). If QH is directed upward, corresponding to positive Tw-Ta, it can enhance CO2 and CH4 emissions from inland waters, thereby contributing to increased greenhouse gas concentrations in the atmosphere. The students found mostly negative Tw-Ta across small ponds, lakes, streams/rivers and the sea shore (i.e. downward QH), with Tw-Ta becoming increasingly negative with increasing Ta. Further examination of Tw-Ta using high-frequency temperature data from inland waters across the globe confirmed that Tw-Ta is linearly related to Ta. Using the longest available high-frequency temperature time series from Lake Erken, Sweden, we found a rapid increase in the occasions of negative Tw-Ta with increasing annual mean Ta since 1989. From these results, we can expect that ongoing and projected global warming will result in increasingly negative Tw-Ta, thereby reducing CO2 and CH4 transfer velocities from inland waters into the atmosphere.