Data Management & Analysis
Data are entered, verified, stored, and analyzed using the SAS Information System. Data will also be entered into the USEPA STORET system and the NonPoint Source Management System.
Data analysis includes:
- comparisons of concentrations and annual exports of nitrogen, phosphorus, and suspended solids from each of the three watersheds, testing the hypothesis that these parameters are reduced by riparian reforestation
- mass-balance estimates of nitrogen, phosphorus, and sediment retention within the reforested riparian buffer.
Findings to Date
Mass balance estimates obtained from concentration gradients in monitoring-well transects and streamwater exports indicate that, since 1994, the RFBS has removed between 7 and 35% annually of upslope inputs of subsurface nitrate, averaging 26%. Estimated mass removal rates of nitrate have varied between 19 and 155 kg y-1per hectare of buffer area. These rates are consistent with denitrification estimates of ~80 kg ha-1 y-1 made in 1994 and 1995. The temporal trends from both mass balance and the paired-watershed comparison suggest that the nitrate removal began when the buffer area was taken out of agriculture and that the rate of removal did not increase further until 2002. Between 2002 and 2005 nitrate concentration in the RFBS-watershed declined while that in the reference stream only slightly declined from 2004 to 2005. The decline in nitrate concentration in the RFBS-watershed corresponded temporally with the rapid increase in tree growth, but the trend is too recent to evaluate statistically.
Removal of groundwater nitrate by the riparian forest buffer system.
Sediment export from RFBS-watershed declined relative to that from the reference watershed by about 50% between 1997 and 2001, suggesting that the RFBS is increasingly effective in filtering suspended sediments. An independent estimate of suspended sediment removal was obtained from overland flow collectors arrayed in transects. The spreader (Zone 3) reduced suspended solids concentration by 40% (P<0.05), and the combination of the spreader and the reforested buffer (Zones 2 and 3) reduced suspended solids by 52% (P<0.05).
Removal of suspended sediments by the riparian buffer system.