WAVE-INDUCED SHEAR STRESSES, PLANT NUTRIENTS AND CHLOROPHYLL IN 7 SHALLOW LAKES

1. Sediment resuspension dynamics were investigated in relation to cha nges in water column nutrients (TP, TN, PO4-P, NO3-N and NH4-N), chlor ophyll a and phaeopigment in seven shallow (Z(m) < 1.5 m) lakes in Sou th Island, New Zealand, ranging in area from 0.1 to 180 km(2). 2. Bent hic shear stress, calculated from wind speed, effective fetch and dept h, was a considerably better predictor of nutrient and pigment concent rations than wind speed. 3. For TP, TN, chlorophyll a and phaeopigment , sixteen of the possible twenty-eight linear correlations with benthi c shear stress were significant at P < 0.05, with 16-87% of the variat ion being explained by shear stress. 4. Wind decreased the ratios of T N : TP, with ratios exponentially approaching those of the sediments a s shear stress increased in four of the lakes. 5. Relationships of dis solved inorganic nutrients to shear stress were considerably weaker th an those for total nutrients and showed no consistent trend over the s even lakes. 6. Estimated annual mean TP inclusive of resuspension was over four times higher than that derived from measured calm samples in two lakes. 7. The number of nutrient and pigment parameters that were significantly correlated with shear stress and the strengths of the r elationships varied widely from lake to lake. We could establish no si mple relationships between these effects and any single characteristic of the lake, sediment, or water. 8. A function is developed to predic t the rate of entrainment of TN and TP in response to an applied shear stress, where the independent variables are sediment nutrient content and particle size, and the macrophyte density in the lake.