USE OF SEEPAGE METERS TO MEASURE GROUNDWATER-FLOW AT BROOK TROUT REDDS

Anomalous influxes of water into unfilled collection bags can greatly overestimate volume and flow rate data from seepage meters. From stati c tank trials, initially empty collection bags (4,500 mL capacity) att ached to seepage meters gained significantly more water relative to ba gs prefilled to 1,000 mL. Data from a study of groundwater flow at red ds of brook trout Salvelinus fontinalis in Scott Lake, Ontario, indica te that the use of unfilled bags biases seepage meter data. At these r edds, the anomalous influx of water into unfilled bags was significant (intercept of regression equation, y = 275 mL); however, this influx was sufficiently reduced when prefilled bags were used (y = 34 mL). Ou r data suggest that even at high how rates (22-169 mL . m(-2). min(-1) ), seepage measures can be inflated by an order of magnitude when init ially empty bags are used. Because of this anomaly, previous measures of ground water flow at brook trout redds with unfilled bags are proba bly not representative of natural flow rates. Our estimates of groundw ater flow at brook trout redds in Scott Lake (6-296 mL . m(-2). min(-1 )) are very similar to the range in groundwater flow found in lake and stream redds (4-340 mL . m(-2). min(-1)) by other methods. We suggest the use of prefilled collection bags (filled to 1,000 mL) and conform ity in measurement units (mL . m(-2). min(-1)) when groundwater how is measured with seepage meters.