Reaeration in a turbulent stream system

The oxygen concentration in a stream is an important parameter of water quality. Changes in oxygen concentrations can affect various stream organisms including fish. Foresters have become concerned with predicting the impacts of forest activities on oxygen levels in streams. Slash, which accumulates in streams as a result of harvesting activities, is a food source for stream organisms. During aerobic respiration, oxygen is utilized. Under some conditions the oxygen concentration can be depleted below acceptable levels. Large, fish bearing streams are generally well protected by forest practice regulations. For smaller streams without fish populations, the issue is one of downstream impairment of water quality as deoxygenated water enters fish-bearing reaches. A natural process counteracting oxygen depletion is reaeration. Reaeration is the exchange of gases between the atmosphere and water. This process operates to maintain oxygen near the saturation concentration. The change in the oxygen deficit in a stream is a function of the existing deficit and the reaeration rate coefficient. The objective of this study was to develop a predictive equation for the reaeration rate coefficient based on the hydraulic characteristics of stream channels. This is a a first step in developing guidelines to regulate harvesting residues in streams. Seven natural stream sites were selected in Oregon. These sites represented a wide range of hydraulic conditions. The stream reaches were segregated into segments of uniform hydraulic characteristics. Sodium sulfite was injected into the stream to artificially deplete the oxygen concentration. The recovery of the oxygen concentration was used to determine the reaeration rate coefficient. Several models for the reaeration process were tested using regression techniques. Some were models proposed by other investigators and some were developed independently. The predictive equation which fit the data best is a function of the maximum unit energy dissipation rate (ED) and a depth parameter (HD): [equation-see PDF] This equation is consistent with theoretical descriptions of gas exchange phenomena. As the rate of energy dissipation increases in a segment, the turbulence in the segment also increases. Turbulence promotes an increase in the liquid-atmosphere interface area and in the exchange rate of volume elements in the interface. Reaeration is stimulated when deaerated water from the bulk flow of the stream replaces the oxygen saturated water in the surface film. As the area of liquid-atmosphere contact increases, the total flux of oxygen molecules into the depleted fluid volume increases. As the fluid volume increases, the change in concentration for a specific flux of molecules decreases. The depth term (HD) can be used to describe the ratio of the surface area to the volume of fluid in the segment. In this study, the depth term used was the discharge divided by the mean width and maximum velocity. This approach adjusts for dead zones that do not actively mix with the bulk flow. For field applications, predicting the reaeration coefficient for any temperature (T) requires that the slope (s), active width (WD), maximum velocity (UD), and discharge (Q), be measured for uniform stream segments. These variables are combined in the following equation: [equation- see PDF] Using the predicted reaeration rates, estimates of mean segment velocities, biochemical oxygen demand loading, and rates of oxygen demand decay, it is possible to predict the oxygen concentration of a stream moving through and downstream from a harvesting site. The reaeration rate influences the maximum deficit and time required for recovery and can be used to evaluate the risks that debris accumulations pose to water quality

Runoff and Sediment Losses from Annual and Unusual Storm Events from the Alto Experimental Watersheds, Texas: 23 Years After Silvicultural Treatments

Evaluating the potential impacts of intensive silvicultural practices on water quality is critical for establishing the long-term sustainability of contemporary forest management practices. From 1979 to 1985, a study involving nine small (~2.5 ha) forested watersheds was conducted near Alto, Texas in the upper western Gulf-Coastal Plain to evaluate the impacts then-current silvicultural practices on water quality. In the years following the study, silvicultural Best Management Practices (BMPs) including Streamside Management Zones (SMZs) and other erosion control practices evolved and questions arose about the applicability of earlier results to current practices. In 1999, these same watersheds were reinstrumented to evaluate the water quality effects of intensive silviculture using modern BMPs. Three years of pre-treatment data were collected to calibrate the watersheds. During the calibration phase, in June 2001, Tropical Storm Allison struck southeastern Texas, dumping almost 11.8 cm of rainfall on saturated soils in about 3 hours. This single storm event resulted in over 73% of the annual flow and over 95% of the annual sediment for 2001. In a little over three hours, the watersheds clearcut and chopped in 1980 generated over 2.5 times more sediment that the entire year following harvest and site-preparation. 1Comparisons of data from the 1979 Alto Watershed study with pretreatment data from the current study suggest that these watersheds have a high potential for geologic erosion even with mature forest cover. Large natural variation in runoff and sediment makes it difficult to detect treatment effects for these forested watersheds

Runoff of Silvicultural Herbicides Applied Using Best Management Practices

Nine small (2.2 to 2.9 ha) and four large (70 to 135 ha) watersheds in East Texas, USA, were instrumented to compare herbicide runoff under different silvicultural systems with best management practices (BMPs). Two treatments were evaluated: conventional, with clearcutting, aerial herbicide site preparation, and hand-applied banded herbaceous release; and intensive, in which subsoiling, aerial fertilization, and a second-year aerial herbicide application were added. Herbicides were applied as operational tank mixes. The highest imazapyr concentration found in stream water was 39 mg L‑1 during the first storm after application (23 days after treatment, DAT) and in-stream concentrations during runoff events dropped to L‑1 in all streams by 150 DAT. The highest hexazinone concentration was 8 mg L‑1 for the banded application and 35 mg L‑1 for the broadcast application the following year and fell to L‑1 in all streams by 140 DAT. The highest sulfometuron methyl concentration found during a runoff event was 4 mg L‑1 and fell to L‑1 in all streams by 80 DAT. About 1 to 2% of applied imazapyr and less than 1% of hexazinone and sulfometuron methyl were measured in storm runoff. Herbicide was found in streams during storm events only (all herbicides wereµg/L in all true baseflow samples), and peak concentrations during runoff events persisted for relatively short times (\u3c 24 h). These results suggest that silvicultural herbicide applications implemented with contemporary BMPs are unlikely to result in chronic exposure of aquatic biota; therefore, herbicide use under these conditions is unlikely to degrade surface waters

Alsea watershed study revisited: unpublished temperature datasets from pre-harvest 2006 to 2010

These data contain temperature readings from dataloggers launched in Deer Creek, Flynn Creek, and Needle Branch from 2006 to 2010. These loggers were apart of the Alsea Watershed Revisisted Study Revisited articles, but the data was incomplete due to logging gaps, temperature spikes, or other issues. The "Thermistor Functionality" datasets indicate whether dataloggers launched in each stream have complete datasets or not. Despite these data not being complete, they help tell the data collection story for the Alsea Watershed Study Revisited

Characterizing granular material in aerial application

The ASTM Standard: Standard Test Method for Particle Size Distribution of Granular Carriers and Granular Pesticides (E726-01) is the only ASTM standard that specifically addresses the characterization of nonspherical particles. To our knowledge there is no standard for particle size distribution measurements by laser diffraction or for particle sphericity measurements by any means to complete the description of the granular material. The present paper reviews a modeling effort that effectively characterizes and then represents the behavior of nonspherical particles during aerial application, highlights the difficulties inherent in interpreting light scattering by nonspherical particles, and suggests a laboratory experiment that accurately recovers particle sphericity. Model revisions enable the user to select the granular application technique from a menu of options once the granular material has been adequately parameterized. Quantitative comparisons are made with available field data to demonstrate the implementation of the several available granular material delivery systems. Notice is made that a standard should be developed for measuring (1) particle size distributions using laser diffraction instruments, and (2) particle sphericity with a technique suggested in the paper

Nitrogen and phosphorus concentrations in forest streams of the United States

Seventy to eighty percent of the water flowing in rivers in the United States originates as precipitation in forests. This project developed a synoptic picture of the patterns in water chemistry for over 300 streams in small, forested watersheds across the United States. Nitrate (NO3-) concentrations averaged 0.31 mg N/L, with some streams averaging ten times this level. Nitrate concentrations tended to be higher in the northeastern United States in watersheds dominated by hardwood forests (especially hardwoods other than oaks) and in recently harvested watersheds. Concentrations of dissolved organic N (mean 0.32 mg N/L) were similar to those of NO3-, whereas ammonium (NH4+) concentrations were much lower (mean 0.05 mg N/L). Nitrate dominated the N loads of streams draining hardwood forests, whereas dissolved organic N dominated the streams in coniferous forests. Concentrations of inorganic phosphate were typically much lower (mean 12 mg P/L) than dissolved organic phosphate (mean 84 mg P/L). The frequencies of chemical concentrations in streams in small, forested watersheds showed more streams with higher NO3- concentrations than the streams used in national monitoring programs of larger, mostly forested watersheds. At a local scale, no trend in nitrate concentration with stream order or basin size was consistent across studies

Water Quality Effects of Clearcut Harvesting and Forest Fertilization with Best Management Practices

Nine small (2.5 ha) and four large (70–135 ha) watersheds were instrumented in 1999 to evaluate the effects of silvicultural practices with application of best management practices (BMPs) on stream water quality in East Texas, USA. Two management regimes were implemented in 2002: (i) conventional, with clearcutting, herbicide site preparation, and BMPs and (ii) intensive, which added subsoiling, aerial broadcast fertilization, and an additional herbicide application. Watershed effects were compared with results from a study on the same small watersheds in 1981, in which two combinations of harvesting and mechanical site preparation without BMPs or fertilization were evaluated. Clearcutting with conventional site preparation resulted in increased nitrogen losses on the small watersheds by about 1 additional kg ha−1 each of total Kjeldahl nitrogen (TKN) and nitrate-nitrogen (NO3–N) in 2003. First-year losses were not significantly increased on the large watershed with a conventional site preparation with BMPs. Fertilization resulted in increased runoff losses in 2003 on the intensive small watersheds by an additional 0.77, 2.33, and 0.36 kg ha−1 for NO3–N, TKN, and total phosphorus, respectively. Total loss rates of ammonia nitrogen (NH4–N) and NO3–N were low overall and accounted for only ∼7% of the applied N. Mean loss rates from treated watersheds were much lower than rainfall inputs of about 5 kg ha−1 TKN and NO3–N in 2003. Aerial fertilization of the 5-yr-old stand on another large watershed did not increase nutrient losses. Intensive silvicultural practices with BMPs did not significantly impair surface water quality with N and P