Publication documents nutrient concentrations in small headwater streams following forestry operations using modern best management practices

Nutrient concentrations in streams is often an important aspect of watershed nutrient management, total maximum daily loads, and surface water supply protection. However, there are few studies of nutrient release following forestry operations implemented using modern best management practices (BMPs).

A recent publication reports results from a study that evaluated the effects of modern forest operations (harvest, yarding, site preparation, planting, and competition control with BMPs) in loblolly pine forests on nutrient concentrations and yields in adjacent small headwater streams. The study also sought to assess whether Georgia’s BMPs were effective in protecting chemical water quality at the watershed scale. The study was conducted on lands formerly owned by International Paper with support from International Paper, NCASI, and others.

The authors conclude that “[with] the application of modern BMPs, changes in nutrient concentrations due to timber harvest and planting were modest or statistically insignificant.” 

The abstract for the paper follows.

“Timber harvest temporarily increases water yield; however, relationships between hydrologic and nutrient chemistry changes have not been consistent. This study quantified the effects of forest harvesting and site preparation without fertilization and with modern best management practices on nutrient concentrations and yields in small headwater streams of the Southeastern Coastal Plain. We monitored two watershed pairs for 2 years prior to and 1 year following timber harvest and for 2 more years following site preparation and planting. Treatment watersheds were clearcut, and downstream portions of streamside management zones were thinned in Fall 2003. Site preparation (herbicide application and burning) and planting followed a year later. All operations followed 1999 Georgia forestry best management practices. Previously published research revealed a large increase in water yield following harvest. Nutrient concentrations varied significantly within and between monitoring periods, even in reference watersheds. Silvicultural activities had no discernible effect on phosphorus and ammonium concentrations; however, statistically significant increases in nitrate/nitrite (67–340 μgL-1) and total nitrogen concentrations (100–400 μgL-1) in treatment watersheds followed stand re-establishment. Nutrient yields increased after timber harvest largely as a result of increased water yields, although increased nutrient yields were small relative to inter-annual and inter-watershed variability and variability. Annual water yield largely explained the variability in annual nitrogen and phosphorus export from reference and treatment streams (r2 values from 0.65 to 0.98). High NOx concentrations coming from an upstream agricultural area decreased 1600–1800 μgL-1 over several hundred metres in the treatment streams by dilution, uptake or denitrification.”

Reference 

Marchman, S.C., M. Miwa, W.B. Summer, S. Terrell, D.G. Jones, S.L. Scarbrough, and C.R. Jackson. 2015. Clearcutting and pine planting effects on nutrient concentrations and export in two mixed use headwater streams: Upper Coastal Plain, Southeastern USA. Hydrological Processes 29:13–28. http://dx.doi.org/10.1002/hyp.10121