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"Chang, Mingteh"
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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.
Journal Article
Runoff of Silvicultural Herbicides Applied Using Best Management Practices
Nine small (2.2-2.9 ha) and four large (70-135 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 2nd-year aerial herbicide application were added. Herbicides were applied as operational tank mixes. The highest imazapyr concentration found in stream water was 39 μg L-1 during the first storm after application (23 days after treatment [DAT]) and in-stream concentrations during runoff events dropped to <1 μg L-1 in all streams by 150 DAT. The highest hexazinone concentration was 8 μg L-1 for the banded application and 35 μg L-1 for the broadcast application the following year and fell to <1 μg L-1 in all streams by 140 DAT. The highest sulfometuron methyl concentration found during a runoff event was 4 μg L-1 and fell to <1 μg L-1 in all streams by 80 DAT. Approximately 1-2% of applied imazapyr and <1% of hexazinone and sulfometuron methyl were measured in storm runoff. Herbicide was found in streams during storm events only (all herbicides were <1 μg L-1 in all true baseflow samples), and peak concentrations during runoff events persisted for relatively short times (<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.
Journal Article
Preliminary observations on water quality of storm runoff from four selected residential roofs
Storm runoff from four characteristic types of residential roofs and incident rainwater were monitored for 47 storm events over a six-month period at Nacogdoches, Texas, to study water quality conditions for 20 element and four chemical variables. The total element concentration in storm runoff from each roof type was greater than that of rainwater in the open. Differences in element concentrations in storm runoff among the four roof types were statistically significant ( alpha less than or equal to 0.05) with the differences for the wood shingle roof being the greatest and that for terra cotta clay roof being the least. The median concentrations of four element variables exceeded the Texas surface water quality standards, while 12 variables exceeded the standards at least one time in all samples collected. Zinc concentrations violated the Standard ranging from 85.7 percent of the samples for the wood shingle roof to 66.0 percent for the composite shingle, the greatest exceedances of all 24 variables studied. Storm characteristics and gutter maintenance level had some effects on these water quality conditions. The study suggested that roof types can be important to water pollution management programs. More detailed studies on roof water quality in major municipalities are required.
Conference Proceeding
Applying Cluster Merging and Dynamic Routing Mechanisms to Extend the Lifetime of Wireless Sensor Networks
In recent years, the applications of wireless sensor networks have increased steadily. Sensor nodes are often scattered outdoors and their energy consumption depends heavily on the area of coverage and network topology. Many studies were focused on saving the energy of sensor nodes to maintain their functionality. This work aims at extending the lifetime of a wireless sensor network by using cluster merging and dynamic routing mechanisms. Cluster merging can increase the number of sensor nodes in a cluster to balance its energy consumption; dynamic routing prevents the cluster heads from exhausting electric power by forwarding data through detoured routes. The simulation results show that cluster merging followed by dynamic routing is more efficient in extending network lifetime. The best combination of the above two mechanisms is to set the threshold of the remaining energy to 90% for applying cluster merging and 10% for applying dynamic routing, which results in the lifetime about 9 times that of a wireless sensor network without using the adaptive mechanisms. [PUBLICATION ABSTRACT]
Journal Article