Aquatic systems throughout many parts of British Columbia have been impaired by human activity, and they continue to deteriorate despite legal mandates such as the B.C. Water Protection Act and the Forest Practices Codes, and massive expenditures such as Forest Renewal British Columbia. Identifying specific impacts to stream ecosystems can be challenging, and determining the causes of those impacts even more difficult. Impacts are often cumulative, meaning that small impacts accumulate to have large effects. Characterization and quantification of cumulative watershed effects are essential if land-use activities and restoration projects are to be designed to minimize deterioration. The standardized methods of cumulative effects analysis tend to be too time consuming and expensive to be practical. This study examines the utility of analysing diurnal dissolved oxygen and pH cycles for assessment of cumulative effects of forest harvesting on stream ecology. These diurnal cycles, observed with continuous monitoring, can be largely driven by stream metabolism (photosynthesis and respiration), and thereby used as a measure of whole-stream productivity and, potentially, the cumulative effects on productivity resulting from forest harvesting. Water temperature, pH, and dissolved oxygen were monitored continuously from 2002 to 2004 in three relatively undeveloped first order streams in the southern coast region of British Columbia. Diurnal oscillations were detected for each parameter in all three streams, and noted to each have similar amplitudes between streams. Water temperature tended to oscillate diurnally by, on average, approximately 1oC during winters and more than 2oC during summers. Dissolved oxygen and pH oscillations showed little seasonal variability, averaging roughly 0.6 mg/L and 0.10 pH units respectively across seasons. Their diurnal cycles were near mirror images (opposite phases) of those in water temperature, suggesting that the observed diurnal changes were caused primarily by changes in water temperature rather than by photosynthetic activity. This was confirmed by net daily metabolism estimates, and is likely explained by low biomass and high re-aeration in these streams. It was therefore determined that this technique is not suitable for measuring stream productivity, or cumulative effects upon it, in the relatively unproductive streams of coastal British Columbia. The technique was, however, shown to be useful in streams with high productivity and low re-aeration, and therefore may be useful for measuring cumulative effects in forested streams in the interior of British Columbia.
Quilty, Edward J., Richardson, John S.; Farahmand, Touraj. 2005. 'Ephects' - a cumulative effects assessment tool using automated continuous pH measurements in streams. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), Riparian, Ecology, British, Columbia
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