John-Mark Davies

Effects of Water Level Fluctuation and Short-Term Climate Variation on Thermal and Stratification Regimes of a British Columbia Reservoir and Lake

ABSTRACT Stratification and thermal regimes of a reservoir with fluctuating water levels were compared to a natural lake of similar morphometry and trophic status over a two-year period (2000–2001) in coastal British Columbia, Canada. We compared the timing and duration of stratification, summer heat budgets and heat fluxes in two morphometrically contrasting basins of Sooke Lake Reservoir and Shawnigan Lake (one shallow and one deep basin per water body). In the second year of the study, a 100-year drought allowed us to compare responses of a reservoir and a lake to contrasting years of climatic conditions. Loss of volume from the reservoir during summer and fall caused stratification and thermal regimes to differ from Shawnigan Lake, but the magnitude of these differences was mediated by basin morphometry. Duration of summer stratification, timing of heat content, and the relative importance of seasonal heat fluxes in the shallow basin of Sooke Lake Reservoir were most different from Shawnigan Lake. While there were no major differences between years for Shawnigan Lake, contrasting years in precipitation and hydrology caused Sooke Lake Reservoir stratification and thermal regimes to differ between years. The magnitude of differences between years was mediated by basin size, with the shallower reservoir basin having greater differences between years. Our results indicate that reservoir physical processes are sensitive to short-term changes in hydrology, and that the combined impacts of short-term climate variation and anthropogenic manipulation of hydrology may be greater in shallow reservoir ecosystems.

Initial Measurements of Benthic Photosynthesis and Respiration in Lake Erie

The first reported in situ measurements of benthic primary production in Lake Erie were made on rocky substrata using oxygen and dissolved inorganic carbon change in 1997 and 1998. The productivity quotient for net benthic algal growth was determined to be 1.1 based on contemporaneous measurement of oxygen production and carbon uptake. Highest rates of gross photosynthesis were > 300 mg O2/m2/h on rocky substrata with mixed stands of Cladophora and dreissenid mussels. These stands also exhibited the greatest rates of oxygen consumption in the dark. Bare rock substrata had lower rates of gross photosynthesis than rock occupied by mussels or Cladophora, but even these habitats had rates that would place them among the highest rates measured in fresh water. Areal benthic photosynthetic rates would greatly exceed areal pelagic photosynthesis in depths shallower than 5 m depth in the eastern basin; and, at greater depths, the importance of declining benthic areal photosynthesis relative to generally increasing integral pelagic production with depth would depend on substratum type and water clarity. Dreissenid mussels had a positive effect on benthic photosynthesis that was especially evident in stimulating Cladophora growth over the course of the 1998 season.

Temporal discontinuity of nutrient limitation in plankton communities

Ideas on how various measures of nutrient limitation relate to plankton biomass and species composition are re-examined. While long-term and multi-lake studies typically focus on determining overall biomass, seasonal studies are more focused toward understanding species composition. We use physiological assays to assess short-term nutrient deficiency of nitrogen and phosphorus in two moderately fertile lakes. While biomass in the lakes was considered to ultimately be limited by total phosphorus, nutrient assays were variable in time. Nutrient ratios (TN:TP, PN:PP, PC:PP and PC:PN) did not predict short-term deficiencies, notably that nitrogen deficiency occurred in these phosphorus-limited lakes. In one of our study lakes, there was a relaxation of phosphorus deficiency despite phosphate concentrations occurring below traditional detection limits. Following this period, there was an autumn bloom of Aphanizomenon flos-aquae. This relationship corresponds with other studies that have found A. flos-aquae to be a poor competitor for phosphorus. In contrast, phosphorus deficiency remained high prior to the autumn diatom bloom in our other study lake. Deficiency measures remain an excellent means of assessing physiological status of plankton communities and provide greater insight into species compositional changes, especially when other potential indicators like dissolved nutrient concentrations are inconclusive. Regardless of the nutrient limitation indicator used for a given study, it is critical to consider the appropriate scale of the measure.

A comparison of phosphorus deficiency indicators with steady state phosphate in lakes

A fundamental step in the management of nutrient impacted water bodies is the determination of the type and degree of nutrient limitation. However, nutrient deficiency indicators often provide inconsistent results. Recent advances in the measurement of phosphate concentrations may provide a better means to understand results from P deficiency indicators. With regards to phosphorus, deficiency indicators should predict P-limitation when phosphate concentrations are consistently low. We use this new understanding to examine the relationships between phosphate concentration and P deficiency. Patterns of steady state phosphate (ssPO(4)(3-)) concentrations and P deficiency were evaluated in 109 lakes located across Canada. Lakes encompassed a broad range in TP concentration (1.79-139.7 μg L(-1)). The relationships between ssPO(4)(3-) concentrations and simultaneously measured total P (TP), total dissolved P (TDP) and soluble reactive P (SRP) concentrations, particulate C:P and N:P ratios, alkaline phosphatase activities (APA) and phosphate turnover times (TT) were analyzed. ssPO(4)(3-) was positively correlated with TP and TDP. The ssPO(4)(3-) concentrations were 2-3 orders of magnitude lower than SRP concentrations. These two measures were only weakly correlated, suggesting that SRP is a major overestimate of PO(4)(3-). The ssPO(4)(3-) concentrations were negatively correlated with C:P and N:P ratios, and with APA, consistent with expectations. When only lakes with TT < 15 min were considered, TT was negatively correlated with TP, challenging the idea that nutrients become less limiting in more eutrophic systems. Overall, P deficiency indicators related to ssPO(4)(3-) in the expected manner. However, variability in relationships with APA and particulate stoichiometry emphasize the need for cautious interpretation of P deficiency measurements. We recommend simultaneous use of multiple techniques to confidently assess P deficiency.

Application and Tests of the Canadian Water Quality Index for Assessing Changes in Water Quality in Lakes and Rivers of Central North America

Abstract The Canadian Water Quality Index (CWQI) is a tool for communicating information to the general public and governments about water quality and assessing changes in water quality over time. It has been adopted for national and provincial reporting on water quality within Canada. It is used in this study to describe changes in water quality along a prairie river system and to assess changes in river water quality prior to and after the installation of tertiary clarifiers for the removal of phosphorus from wastewater effluent. CWQI values reflected the composite assessment of changes in individual parameter concentrations along the river. There was a slight increase in the CWQI after the installation of tertiary clarifiers, which reflected the improvement of only a few components of the wastewater. Several weaknesses of the CWQI were explored, including susceptibility to sample number per index period. A sound sampling design should form the basis of any monitoring program and, to a large extent, CWQI values are a reflection of the sampling program.

Interfacing Stakeholder Involvement into a Surface Water-Quality Modelling System for Water Management and Policy Development

Water quality has been under unprecedented pressure over the past few decades due, in part, to increasing nutrient pollution from cities, industrial zones and agricultural areas entering river systems. The dynamics of these impacts on water quality are complex and stem from decisions and activities of different groups of stakeholders, who can have different business plans, values and attitudes towards water quality. This means that, improving the quality of water requires incorporating stakeholders’ viewpoints and decisions into water quality management processes. This study proposes a modelling framework to engage stakeholders in selecting practices and policies that can improve riverine and lacustrine water quality.

Macroinvertebrate communities in a Northern Great Plains river are strongly shaped by naturally occurring suspended sediments: implications for ecosystem health assessment

Rivers are typified by considerable seasonal flow variability. In rivers that flow through alluvial deposits, fine sediment (<63 μm) is readily suspended, especially during periods of high discharge. Therefore, assessment of the effects on biota of anthropogenic stressors must occur within the context of dynamic turbidity and background flow conditions. We used the Qu’Appelle River in southern Saskatchewan as a study system for which we developed a model in which discharge is a principal determinant of in-stream suspended sediment. We explored this relationship with a case study showing that macroinvertebrate community structure was strongly correlated with suspended sediment gradients and, ultimately, predicted by discharge. Factors affecting sediment loads and ecosystem responses in managed systems should be considered so that in-stream water quantity and quality needs are met. This new understanding should enable development of improved ecosystem-based flow-management objectives.