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Fig. 12. Time required to detect reductions in total nitrogen load at Kinston for p-values of 0.1 (bottom), 0.05 (middle), and 0.01 (top). (The Bayesian analogue would be posterior Bayes factors of 54 and respectively.) 24 ree ies Fig. 11. Median concentration from 1988 to 1997 divided by median concentration from 1979 to 1987, for each of the seven monitoring stations depicted in Fig. 1. Circles indicate the Falls Lake (station 1), Clayton (station 2), and Kinston (station 5) stations.

Figure 12 Time required to detect reductions in total nitrogen load at Kinston for p-values of 0.1 (bottom), 0.05 (middle), and 0.01 (top). (The Bayesian analogue would be posterior Bayes factors of 54 and respectively.) 24 ree ies Fig. 11. Median concentration from 1988 to 1997 divided by median concentration from 1979 to 1987, for each of the seven monitoring stations depicted in Fig. 1. Circles indicate the Falls Lake (station 1), Clayton (station 2), and Kinston (station 5) stations.

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Fig. 1. Neuse River watershed and location of the seven monitoring stations. Triangles indicate the location of urban areas.
Fig. 1. Neuse River watershed and location of the seven monitoring stations. Triangles indicate the location of urban areas.
Fig. 2. Estimates of annual anthropogenic phosphorus sources within the watershed from cropland, animals, and point sources. The vertical dotted line represents the first year for which loading estimates were calculated. Annual Nows varied considerably at each station from 1979 to 1998 (Fig. 4). Though no trends are apparent, the completion of the Falls Lake dam in 1983 removed extreme high and low daily flows at both the Falls Lake and Clayton stations (not shown). Mean flows at the Falls Lake, Clayton, and Kinston stations since the dam completion (1984-1998) have been 87, 97, and 99%, respectively, of the mean flows before dam completion (1979-— 1983), suggesting slight evaporative losses resulting from the reservoir creation. Mean flows at the Falls Lake, Clayton and Kinston stations since the phosphate detergent ban (1988-1998) have been 92, 104, and 108%, respectively, of the flows prior to the ban (1979-1987). From 1979 to 1998 the Falls Lake station flow has averaged 63 and 25% of the Clayton and Kinston flows, respectively, and the Clayton station flow has averaged 40% of the Kinston station flow, consistent with the relative sizes of each station’s subwatershed.
Fig. 2. Estimates of annual anthropogenic phosphorus sources within the watershed from cropland, animals, and point sources. The vertical dotted line represents the first year for which loading estimates were calculated. Annual Nows varied considerably at each station from 1979 to 1998 (Fig. 4). Though no trends are apparent, the completion of the Falls Lake dam in 1983 removed extreme high and low daily flows at both the Falls Lake and Clayton stations (not shown). Mean flows at the Falls Lake, Clayton, and Kinston stations since the dam completion (1984-1998) have been 87, 97, and 99%, respectively, of the mean flows before dam completion (1979-— 1983), suggesting slight evaporative losses resulting from the reservoir creation. Mean flows at the Falls Lake, Clayton and Kinston stations since the phosphate detergent ban (1988-1998) have been 92, 104, and 108%, respectively, of the flows prior to the ban (1979-1987). From 1979 to 1998 the Falls Lake station flow has averaged 63 and 25% of the Clayton and Kinston flows, respectively, and the Clayton station flow has averaged 40% of the Kinston station flow, consistent with the relative sizes of each station’s subwatershed.
Fig. 3. Estimates of annual anthropogenic nitrogen sources within the watershed from cropland, animals, and point sources. The vertical dotted line represents the first year for which loading estimates were calculated.
Fig. 3. Estimates of annual anthropogenic nitrogen sources within the watershed from cropland, animals, and point sources. The vertical dotted line represents the first year for which loading estimates were calculated.
Fig. 4. Total yearly flow at the Falls Lake dam (bottom), Clayton (middle), and Kinston (top) stations.
Fig. 4. Total yearly flow at the Falls Lake dam (bottom), Clayton (middle), and Kinston (top) stations.
Fig. 5. Box-and-whisker plots of total phosphorus concen- tration data collected within a given year. Each box represents the inter-quartile range, the line through the box represents the median, the dot represents the sample mean, and the whiskers represent outliers within 1.5 times the inter-quartile range. The width of the box corresponds to the number of samples relative to other years at that station.
Fig. 5. Box-and-whisker plots of total phosphorus concen- tration data collected within a given year. Each box represents the inter-quartile range, the line through the box represents the median, the dot represents the sample mean, and the whiskers represent outliers within 1.5 times the inter-quartile range. The width of the box corresponds to the number of samples relative to other years at that station.
Fig. 6. Box-and-whisker plots of total nitrogen concentra- tion data collected within a given year. Each box represents the inter-quartile range, the line through the box represents the median, the dot represents the sample mean, and the whiskers represent outliers within 1.5 times the inter- quartile range. The width of the box corresponds to the number of samples relative to other years at that station.
Fig. 6. Box-and-whisker plots of total nitrogen concentra- tion data collected within a given year. Each box represents the inter-quartile range, the line through the box represents the median, the dot represents the sample mean, and the whiskers represent outliers within 1.5 times the inter- quartile range. The width of the box corresponds to the number of samples relative to other years at that station.
Fig. 7. Estimated yearly total phosphorus loads +two standard errors.
Fig. 7. Estimated yearly total phosphorus loads +two standard errors.
Table 1. Summary of models used to estimate annual loads elevated at Kinston from approximately 1990-1995, but the trends are not consistent like the trends at Clayton. Nitrate and TKN loads at Kinston are close over the entire period, with neither demonstrating clear patterns (Fig. 9). Flow-adjusted concentrations indicate the TKN concentration has generally decreased over the entire period, but nitrate concen- tration has varied (Fig. 10). The flow-adjusted total nitrogen concentration has also varied with no overall trend.
Table 1. Summary of models used to estimate annual loads elevated at Kinston from approximately 1990-1995, but the trends are not consistent like the trends at Clayton. Nitrate and TKN loads at Kinston are close over the entire period, with neither demonstrating clear patterns (Fig. 9). Flow-adjusted concentrations indicate the TKN concentration has generally decreased over the entire period, but nitrate concen- tration has varied (Fig. 10). The flow-adjusted total nitrogen concentration has also varied with no overall trend.
Fig. 9. Estimated yearly total nitrogen (circle), nitrate (triangle), and TKN (square) loads + two standard errors. Nitrate median ratios indicate a pattern opposite that of the phosphorus median ratios (Fig. 11). Nitrate increases at Clayton (station 2) diminish downstream, returning to approximately pre-1988 concentrations by Kinston (station 5). The reason for the diminishing nitrate increase may in part be the same as the reason for the diminishing phosphorus decrease. While controls targeting phosphorus have reduced point-source phosphorus discharges, point-
Fig. 9. Estimated yearly total nitrogen (circle), nitrate (triangle), and TKN (square) loads + two standard errors. Nitrate median ratios indicate a pattern opposite that of the phosphorus median ratios (Fig. 11). Nitrate increases at Clayton (station 2) diminish downstream, returning to approximately pre-1988 concentrations by Kinston (station 5). The reason for the diminishing nitrate increase may in part be the same as the reason for the diminishing phosphorus decrease. While controls targeting phosphorus have reduced point-source phosphorus discharges, point-
Fig. 10. Yearly average flow-adjusted total nitrogen (circle), nitrate (triangle), and TKN (square) concentrations + one standard error. Data from the Falls Lake station are not shown due to lack of a significant flow: concentration relationship.
Fig. 10. Yearly average flow-adjusted total nitrogen (circle), nitrate (triangle), and TKN (square) concentrations + one standard error. Data from the Falls Lake station are not shown due to lack of a significant flow: concentration relationship.
Related topics:
Nutrient ManagementTotal PhosphorusTrend detection
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