Modelling the response of a highly eutrophic lake to reductions in external and internal nutrient loading

Abstract

The reduction of macronutrients to levels that limit primary production is often a critical element of mitigating eutrophication and reducing the potential for algal blooms. Lake Okaro has remained highly eutrophic despite an intensive catchment and in-lake restoration programme, including implementation of a constructed wetland, riparian protection, an alum application and application of a modified zeolite mineral (Z2G1) to reduce internal nutrient loading. A onedimensional process-based ecosystem model (DYRESM-CAEDYM) was used in this study to investigate the need for further nutrient loading reductions of both nitrogen (N) and phosphorus (P). The model was calibrated against field data for a 2-year period and validated over two separate 1-year periods. Model simulations suggest that the trophic status of the lake, measured quantitatively with the Trophic Level Index (TLI), could shift from highly eutrophic to mesotrophic with external and internal loads of both N and P reduced by 75Á90%. The magnitude of the nutrient load reductions is indicative of a major challenge in being able to effect transitions across trophic state categories for eutrophic lakes.

Advancing projections of phytoplankton responses to climate change through ensemble modelling

“…Such oscillations do not appear in observations, nor in PCLake and PROTECH during summer months, and consequently the r 2 values achieved for DYRESM-CAEDYM were generally low (as also seen in other applications of this model, e.g., Trolle et al, 2011;Özkundakci et al, 2011). In contrast to PCLake and PROTECH, DYRESM-CAEDYM includes detailed high-frequency hydrodynamics, which can influence phytoplankton concentrations and vertical distributions in the short-term (sub-daily and daily), and thus generally cause greater output variability.…”

Modelling catchment management impact on in-stream phosphorus loads in northern Victoria

“…Effective management of phosphorus loads requires consideration of the complex interactions between terrestrial and aquatic exchanges, the physico-chemical properties of phosphorus forms, existing water quality conditions, nutrient targets for aquatic health, and trade-offs between economic returns associated with anthropogenic activities and environmental pollution (McDowell et al, 2004;Davis and Koop, 2006;Cherry et al, 2008;Heathwaite, 2010;Özkundakci et al, 2011;Doole et al, 2011;Panagopoulos et al, 2011). Phosphorus moves in the landscape in either a dissolved form, i.e.…”

Parameterisation of sediment geochemistry for simulating water quality responses to long-term catchment and climate changes in polymictic, eutrophic Lake Rotorua, New Zealand

“…In the case of Lake Rotorua (Rutherford et al [6]) calculated a time for near-complete equilibrium of sediments of up to 195 years, but noted quite rapid and substantial reductions in sediment nutrient releases, because of reduced levels of both nutrient loading and deoxygenation in the water column, with associated improvements in water quality. The lack of feedback between the water column and the bottom sediment composition in the current version of CAEDYM has been described previously, but has not been adequately accounted for in past lake model simulation efforts (Trolle et al [8]; Özkundakci et al [9]). …”

“…Several applications have been made of DYRESM-CAEDYM to different lakes (e.g. Burger et al [7]; Trolle et al [8]; Gal et al [13]; Özkundakci et al [9]) and these publications have detailed descriptions of the model equations.…”

“…The ecological model CAEDYM has a relatively simple process representation of sediment nutrient dynamics even though it has proven remarkably successful in reproducing seasonal changes in concentrations of nutrients in lake bottom waters induced from sediment releases (e.g. Burger et al [7]; Trolle et al [8]; Özkundakci et al [9]). The model regulates the sediment phosphate and ammonium releases according to concentrations of dissolved oxygen (DO) and nitrate, and water temperature in the overlying water layer.…”