Influences on water quality and abundance of cladophora, a shore-fouling green algae, over urban shoreline in Lake Ontario

Abstract

Urban centers border western Lake Ontario, the terminus of the Laurentian Great Lakes, impacting water quality on the shores of this oligotrophic lake. The green algae Cladophora proliferates on the shallow lakebed and fouls the shoreline, presenting an eutrophication concern. The conditions over a typical urbanized shoreline were studied to assess linkages between Cladophora and area nutrient sources. The most pervasive of the mixing areas of varying extent identified using field sensor measurements was associated with the discharge of treated sewage from aWater Pollution Control Plant (WPCP). Phosphorus and nitrogen were enriched at times near the WPCP diffuser and also in shallow water along the shoreline. Dissolved nutrients were also measured directly above the lakebed in close proximity to Cladophora. Dissolved phosphorus and inorganic nitrogen were higher in proximity to the WPCP diffuser at times, however, spatial patterns were not as clearly aligned with external inputs as the patterns of enrichment in the water column. Biomass distribution of Cladophora was unrelated to nutrient levels in the water column or at the lakebed. Yet, concentrations of phosphorus in Cladophora, an indicator of nutrient sufficiency, were higher near the WPCP diffuser. This disparity, while possibly an artifact of variable loss rates of biomass among locations, may in part stem from variable water clarity among areas. Abundant dreissenid mussels also potentially obscure the effects of nutrient loading on algal biomass if the sequestering of phosphorus from offshore plankton, suggested by periods of onshore circulation, approaches the extent of external loading. Further study of phosphorus flux at the lakebed is required to establish clear linkages between external nutrient loading and algal growth in order to manage the proliferation of Cladophora over urban coastline.