Nutrient Movement in Streamside Management Zones and Piedmont Streams Following Forest Fertilization
Secoges, Joseph Michael
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Many statesâ Best Management Practices (BMP) programs established Streamside Management Zone (SMZ) widths based on limited or inadequate data with regard to nutrient fluxes from silvicultural activities. Previous studies in forested watersheds have shown slight post-harvest increases of several nutrients in streams. Also, in agricultural settings, increased nitrogen (N) and phosphorous (P) levels have been detected in streams. However, little is known about the effectiveness of recommended forested SMZ widths for controlling nutrient fluxes following fertilizer application. Diammonium phosphate (DAP) and urea fertilizers were applied to subwatersheds of 2 to 3 year-old loblolly pine (Pinus taeda L.) plantations upslope from SMZ study areas throughout Buckingham Co., VA. Three replications of four SMZ treatment widths (30.5m, 15.2m, and 7.6m plus a thinned 15.2m SMZ) were studied using surface water collectors, cation/anion exchange membranes, lysimeters, and stream grab-samples. Measurement devices were spaced symmetrically across the SMZ from the uphill SMZ edge to stream edge with grab samples being collected approximately 20m upstream and 20m downstream of the fertilized area. Little nitrogen and phosphorous movement was detected in surface water which was monitored using surface water collectors. Near-surface water flow sampling using ionic exchange membranes resulted in our most complete dataset and showed infrequent lateral ion transport in the litter and upper soil layers even after water passed over an approximately 1m wide, seeded firebreak located between the SMZ dripline and fertilized area. Results from lysimeter samples used to measure subsurface flow were limited due to dry conditions; however, the limited samples indicate that only minute levels of nitrogen and phosphorous are transported laterally via shallow subsurface and surface flow. Overall, sampling indicated that only minute quantities of nitrogen and phosphorous were ever transported from the fertilized clearcut to the riparian area. Results indicate that even a 7.6m wide SMZ with a seeded firebreak is adequate to protect streams from industrial fertilizer application in a relatively dry year, but wider SMZs may be necessary for other benefits.
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