Rb. Williamson et al., WATERSHED RIPARIAN MANAGEMENT AND ITS BENEFITS TO A EUTROPHIC LAKE, Journal of water resources planning and management, 122(1), 1996, pp. 24-32
Sediment and nutrient loads from a 73 km(2) mixed pasture/forested wat
ershed that drains to eutrophic Lake Rotorua (New Zealand) were measur
ed before and after diffuse-source controls were implemented. In the p
astoral. areas, these controls were exclusion of grazing (''retirement
'') from the banks of most perennial streams, erosion-prone hillslopes
, and remnant pockets of native forest. After implementation, the load
s changed by -85% for sediment, -27% for particulate P, -26% for solub
le P, -40% for particulate N, and +26% for dissolved N. Calculated tot
al phosphorus specific yields for the pasture portion of the watershed
were 89 kg km(-2) yr(-1) (preimplementation) and 41 kg km(-2) yr(-1)
(postimplementation). When these findings were applied to the whole La
ke Rotorua watershed, we predicted that control measures had reduced T
P loads by 20%. This reduction in phosphorus loads was predicted to re
duce the chlorophyll a concentration by about: 5 mg m(-3), and help sh
ift the lake's trophic state from eutrophic to mesotrophic.