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Influence of Environmental Factors on Biotic Responses to Nutrient Enrichment in Agricultural Streams1

Maret, Terry R., Christopher P. Konrad, and Andrew W. Tranmer, 2010. Influence of Environmental Factors on Biotic Responses to Nutrient Enrichment in Agricultural Streams. Journal of the American Water Resources Association (JAWRA) 46(3):498-513. DOI: 10.1111/j.1752-1688.2010.00430.x Abstract: The influence of environmental factors on biotic responses to nutrients was examined in three diverse agricultural regions of the United States. Seventy wadeable sites were selected along an agricultural land use gradient while minimizing natural variation within each region. Nutrients, habitat, algae, macroinvertebrates, and macrophyte cover were sampled during a single summer low-flow period in 2006 or 2007. Continuous stream stage and water temperature were collected at each site for 30 days prior to sampling. Wide ranges of concentrations were found for total nitrogen (TN) (0.07-9.61 mg/l) and total phosphorus (TP) (<0.004-0.361 mg/l), but biotic responses including periphytic and sestonic chlorophyll a (RCHL and SCHL, respectively), and percent of stream bed with aquatic macrophyte (AQM) growth were not strongly related to concentrations of TN or TP. Pearson’s coefficient of determination (R²) for nutrients and biotic measures across all sites ranged from 0.08 to 0.32 and generally were not higher within each region. The biotic measures (RCHL, SCHL, and AQM) were combined in an index to evaluate eutrophic status across sites that could have different biotic responses to nutrient enrichment. Stepwise multiple regression identified TN, percent canopy, median riffle depth, and daily percent change in stage as significant factors for the eutrophic index (R² = 0.50, p < 0.001). A TN threshold of 0.48 mg/l was identified where eutrophic index scores became less responsive to increasing TN concentrations, for all sites. Multiple plant growth indicators should be used when evaluating eutrophication, especially when streams contain an abundance of macrophytes.     

CHARACTERIZATION OF PARTICULATE MATTER EMISSION FROM OPEN BURNING OF RICE STRAW

Emission from field burning of crop residue, a common practice in many parts of the world today, has potential effects on air quality, atmosphere and climate. This study provides a comprehensive size and compositional characterization of particulate matter (PM) emission from rice straw (RS) burning using both in situ experiments (11 spread field burning) and laboratory hood experiments (3 pile and 6 spread burning) that were conducted during 2003-2006 in Thailand. The carbon balance and emission ratio method was used to determine PM emission factors (EF) in the field experiments. The obtained EFs varied from field to hood experiments reflecting multiple factors affecting combustion and emission. In the hood experiments, EFs were found to be depending on the burning types (spread or pile), moisture content and the combustion efficiency. In addition, in the field experiments, burning rate and EF were also influenced by weather conditions, i.e. wind. Hood pile burning produced significantly higher EF (20±8 g kg(-1) RS) than hood spread burning (4.7±2.2 g kg(-1) RS). The majority of PM emitted from the field burning was PM(2.5) with EF of 5.1±0.7 g m(-2) or 8.3±2.7 g kg(-1) RS burned. The coarse PM fraction (PM(10-2.5)) was mainly generated by fire attention activities and was relatively small, hence the resulting EF of PM(10) (9.4±3.5 g kg(-1) RS) was not significantly higher than PM(2.5). PM size distribution was measured across 8 size ranges (from <0.4 μm to >9.0 μm). The largest fractions of PM, EC and OC were associated with PM(1.1). The most significant components in PM(2.5) and PM(10) include OC, water soluble ions and levoglucosan. Relative abundance of some methoxyphenols (e.g., acetylsyringone), PAHs (e.g., fluoranthene and pyrene), organochlorine pesticides and PCBs may also serve as additional signatures for the PM emission. Presence of these toxic compounds in PM of burning smoke increases the potential toxic effects of the emission. For illustration, an estimation of the annual RS field burning in Thailand was made using the obtained in situ field burning EFs and preliminary burning activity data.     

The regional impacts of small-scale gold mining in Amazonia

Gold mining is the major economic activity in the Upper Tapajós River Basin of the Brazilian Amazon. This article studies the structure, economy and impacts of gold mining operations in this region. Mining has significant environmental impacts in this region resulting in the removal of approximately 67 million m³ of sub-soil per year and accompanied by an annual release of some 12 tons of mercury to air, ground and rivers. In the early 1990s there were 245 mines in operation, employing some 30000 people and producing around 35t gold per year, valued at approximately $400 million yr^-1, the profits being about $110 million yr^-1. Miners spent most of their earnings on local goods and services, while mine owners and merchants in the gold towns invested in land (mainly for ranching), business ventures and money markets. Wealth gained from mining has served as an engine for development in other regions of the world and could, theoretically, achieve the same for Amazonia. However, before this could happen, the Government of Brazil would need to mark a strong presence in the area by providing technical assistance and developing and enforcing mining/environmental regulations. The likelihood of such a development materializing in the foreseeable future is small. In the meantime, gold mining acts, not as an 'engine for development', but as a destabilizing force — provoking environmental damage, social discord and public health hazards in the region.     

Montane Amphibian and Reptile Communities in Madagascar

Abstract; Two habitats in Madagascar, secondary, montane heathland and high plateau prairie, are considered artificial, having been created by human-set fires soon after the island was colonized less than 2000 years ago. These prairie and secondary heathland habitats are also thought to be degraded and faunistically depauperate. To test the depauperate fauna hypothesis we measured levels of herpetofaunal (amphibian and reptile) endemicity between primary forest, montane secondary heathland, and high plateau prairie. We found no species endemic to high plateau prairie, but a significant percentage of the montane herpetofauna is restricted to post-fire secondary heathland. These results support the human-origin hypothesis for prairie, but secondary heathland appears to be a natural, post-fire successional stage that leads to a climax of sclero-phyllous forest. This suggests that careful management of montane heathland could establish new dispersal corridors between currently isolated montane forest blocks and, therefore, could offer new opportunities for conservation in Madagascar. Despite widespread burning, the montane heathlands of Madagascar have diverse herpetofaunal communities, demonstrating that these montane communities are not as seriously degraded as previously believed, and that they may be naturally resistant to fire.     

WATER LEVEL MANAGEMENT OPPORTUNITIES FOR ECOLOGICAL BENEFIT,POOL 5 MISSISSIPPI RWER1

ABSTRACT: This paper examines the potential to manage Mississippi River water levels for ecological benefits. The study focuses on the Weaver Bottoms, a 4,000 acre backwater marsh in southeastern Minnesota (Pool 5) highly valued for fish and wildlife habitat. The Weaver Bottoms has suffered increasing loss of aquatic vegetation and associated habitat degradation since the 1960s, largely due to persistent high water, sedimentation, wave re-suspension of sediments, and poor light penetration. In other reaches of the Mississippi River, water level reductions exposing backwater sediments have produced strong vegetative responses due to subaerial exposure of seeds and sediment compaction. Water level management scenarios for Pool 5 were developed using the HEC-2 water surface profile model. Results indicate that in many years it would be possible to reduce water levels sufficiently to expose much of the Weaver Bottoms, generating a substantial vegetative response. Additional benefits could be expected since both sediment compaction and increased vegetation would reduce re-suspension of sediments. Shifting management priorities to improve habitat would temporarily impact many river users, including both commercial and recreational boaters. Water level reductions must be coordinated with their needs.     

Changes in the quality of river water before, during and after a major flood event associated with a La Niña cycle and treatment for drinking purposes

The treatment of organics present in the lower reaches of a major river system（the Murray–Darling Basin, Australia） before（March–July 2010）, during（December 2010–May 2011） and after（April–December 2012） a major flood period was investigated. The flood period（over 6 months）occurred during an intense La Nia cycle, leading to rapid and high increases in river flows and organic loads in the river water. Dissolved organic carbon（DOC） increased（2–3 times） to high concentrations（up to 16 mg/L） and was found to correlate with river flow rates. The treatability of organics was studied using conventional jar tests with alum and an enhanced coagulation model（mEnCo）. Predicted mean alum dose rates（per mg DOC） were higher before（9.1 mg alum/mg DOC） and after（8.5 mg alum/mg DOC） than during the flood event（8.0 mg alum/mg DOC）,indicating differences in the character of the organics in raw waters. To assess the character of natural organic matter present in raw and treated waters, high performance size exclusion chromatography with UV and fluorescence detectors were used. During the flood period, high molecular weight UV absorbing compounds（〉2 kDa） were mostly detected in waters collected,but were not evident in waters collected before and afterwards. The relative abundances of humic-like and protein-like compounds during and following the flood period were also investigated and found to be of a higher molecular weight during the flood period. The treatability of the organics was found to vary over the three climate conditions investigated.