SAMPLING TECHNIQUES - IMPLICATIONS IN ESTIMATING SUBSTANCE TRANSPORTS FROM SMALL WATERSHEDS
Loads of phosphorus, nitrogen and CODMn have been estimated on an annual basis from two nearby watersheds in central Sweden. The computations were performed according to the following five techniques: 1.Momentary analysis of concentration together with discharge measurements in the middle of a bimonthly period. 2. Momentary analysis of concentration as above but with measurements of mean bimonthly discharge. 3. Momentary analysis of concentration in the middle of each month but with measurements of mean discharge for each month. 4. Linear regression of transport amounts based on monthly runoff values, the relations obtained from old measurements. 5. Yearly areal losses calculated for each element from old measurements valid for different land-types, such as agricultural, forested etc, within each watershed. The third technique was found to be the better technique because runoff- and water quality data were represented most properly. The fourth technique gave close to equal transport amounts as the third, because of significant linear relationships between transport amounts and runoff values.