Periphyton functional and structural response, within semi-natural surrogate streams, to artificially induced water quality perturbations
Date
1993
Authors
Lucey, William Patrick
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Abstract
The concept, design and operation of a standardized, flow-through, split-stream surrogate mesocosm (stream trough) is described within which, in-situ, experimental research was conducted on the contained, biotic component of natural periphyton communities. The surrogate streams enable i) sensitive, sub-lethal and long-term monitoring for detecting environmental impact in ambient waters, and ii) development of standardized protocols for biological toxicity tests and nutrient loading. Siphoned water from a large reservoir supply negates the need for electrically powered pumps; the facility is relatively inexpensive, easily fabricated from Poly-Vinyl-Chloride (PVC) and minimal repair and maintenance is required for year-round operation. Four basic structural components comprise the system including siphon apparatus and header box, manifold supplying water and treatment additives, surrogate streams, and a drainage system.
High quality drinking water drawn from Victoria, British Columbia's Sooke and Humpback Reservoirs, was used in experimental protocols exploring periphyton biomass accrual changes resulting from manipulating phosphorus, nitrogen, light intensity, pH and velocity. How substrata affected accrual was assessed using borosilicate microscope slides, natural river rock and poly-styrofoam sheets. These initial studies sought to elucidate how various stressors affect properties of benthic microalgal communities in-situ, since trough mesocosms permit this complex community to be manipulated using a standardized sampling and processing methodology. The development of a standard method within a conceptual framework was directed toward elucidating the integrating role of periphyton, in shallow lakes and streams, with other ecosystem processes.
Following development of the surrogate streams, a four year field study (1988-1991) quantified the nutrient contribution of sewage effluent (with particular reference to phosphorus), from the resort municipality of Whistler, to the Cheakamus River, British Columbia, Canada. The stream trough study revealed the river's limited phosphorus assimilative capacity, with downstream aesthetics and fisheries habitat adversely affected at periphyton biomass values exceeding 2500 µg/ cm2 (dry weight). Based upon these studies, a Liquid Waste Management Plan (LWMP) recommended effluent discharge directly into the adjacent Squamish River.
A surrogate stream study, on the latter river, in the summer of 1991, was conducted to assess how the effluent diversion would affect water quality, especially with respect to the development of undesirable algal growth. The latter could adversely affect fisheries spawning and rearing habitat downstream of the discharge point. Following a year-long public review of an expanded range of possible L WMP options, enhanced orthophosphorus reduction, using biological tertiary treatment, was adopted. The absence of an adequate database, upon which to model processes effecting biomass accrual, in the Lower Cheakamus River, signals further study of nutrient loading dynamics in both the river and the reservoir, together with an expanded investigation of top-down processes linking herbivory and algal production.
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UN SDG 6: Clean Water and Sanitation