Variation in root density along stream banks

While it is recognized that vegetation plays a significant role in stream bank stabilization, the effects are not fully quantified. The study goal was to determine the type and density of vegetation that provides the greatest protection against stream bank erosion by determining the density of roots in stream banks. To quantify the density of roots along alluvial stream banks, 25 field sites in the Appalachian Mountains were sampled. The riparian buffers varied from short turfgrass to mature riparian forests, representing a range of vegetation types. Root length density (RLD) with depth and aboveground vegetation density were measured. The sites were divided into forested and herbaceous groups and differences in root density were evaluated. At the herbaceous sites, very fine roots (diameter < 0.5 mm) were most common and more than 75% of all roots were concentrated in the upper 30 cm of the stream bank. Under forested vegetation, fine roots (0.5 mm < diameter < 2.0 mm) were more common throughout the bank profile, with 55% of all roots in the top 30 cm. In the top 30 cm of the bank, herbaceous sites had significantly greater overall RLD than forested sites (alpha = 0.01). While there were no significant differences in total RLD below 30 cm, forested sites had significantly greater concentrations of fine roots, as compared with herbaceous sites (alpha = 0.01). As research has shown that erosion resistance has a direct relationship with fine root density, forested vegetation may provide better protection against stream bank erosion.     

Nitrate leaching under grassland as affected by mineral nitrogen fertilization and cattle urine

An experiment was performed to better understand to what extent nitrogen fertilization rate and date and amount of urine deposition, when acting in combination, influence nitrate leaching under grassland. Leaching was studied during two successive winters using 2-m2 grassed lysimeters under three levels of N fertilization (0, 150, and 300 kg N ha(-1) yr(-1), referred to as 0N, 150N, and 300N, respectively), two levels of 15N-labeled urine (105 and 165 kg N ha(-1), referred to as A2 and A3, respectively), and three dates of urine application (spring, summer, and fall). During the first winter, total N leaching losses varied between 2 and 50 kg N ha(-1). When tested in combination, N applied as urine to grassland resulted in three times the total N loss by leaching that occurred following N fertilization in the first winter (4.3, 20.8, 34.9, 14.2, 17.1, and 28.7 kg NO3- -N ha(-1) for no urine, A2, A3, ON, 150N, and 300N, respectively). Leaching of 15N urine significantly depended on the date of application: 6.6, 17.3, and 29.1 kg for spring, summer, and fall, respectively. A similar pattern was observed for the contribution of 15N urine to total N leaching with 4.3, 12.9, and 21.4%. However, urine application, both in terms of amount and date, showed very little long-term effect on these N losses in Year 2. In our conditions of low winter rainfall and drainage, grazing management (through season, urinary N amounts, and urine N concentration) resulted in a higher impact on water nitrate quality than moderate N fertilization management.     

Reducing atrazine losses: water quality implications of alternative runoff control practices

Water quality is being affected by herbicides, some allegedly harmful to human health. Under scrutiny is atrazine (1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine), a commonly used herbicide in corn (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench] production. Concentrations of soluble and adsorbed atrazine losses sometimes exceed the safe drinking water standard of 3 microg L(-1) established by the USEPA. This study assesses the protective implications of runoff control structures and alternative crop farming practices to minimize atrazine losses. Using a computerized simulation model, APEX, the following four practices were the most effective with respect to the average atrazine loss as a percent of the amount applied: (i) constructing sediment ponds, 0.09%; (ii) establishing grass filter strips, 0.14%; (iii) banding a 25% rate of atrazine, 0.40%; and (iv) constructing wetlands, 0.45%. Other atrazine runoff management options, including adoption of alternative tillage practices such as conservation and no-till as well as splitting applications between fall and spring, were marginally effective.     

Assessment of the effectiveness of scup bycatch-reduction regulations in the Loligo squid fishery

Discard reduction is a component of the statutory requirements of the Sustainable Fisheries Act. One species of concern is scup, Stenotomus chrysops, discarded in the Loligo pealei fishery. Initially, regulations were imposed restricting the fishery in time and space to avoid areas and times associated with high scup discarding. Modified gear was required in 2003 on any boat fishing in areas otherwise closed to the fishery to reduce scup discarding. The purpose of this study was to evaluate the success of the 2003 net regulations and the potential influence of time-area closures (GRAs) in achieving a reduction in scup discarding. The regulations are based on three expectations. (1) Reduction in discarding in the Loligo squid fishery will materially reduce total scup discarding. (2) Exclusion of Loligo squid fishing vessels from the GRAs will result in these vessels fishing in areas that inherently produce fewer scup discards without equivalently increasing discarding in other sensitive species. (3) The use of a square-mesh large-mesh section in the extension will reduce scup discarding to the extent that otherwise would be achieved if the boats fished outside the GRAs without the economic cost imposed by redeploying the fleet. Analysis of the NMFS-NEFSC observer database offers no support for the belief that Expectation 1 has been met. Squid catches were too low to sustain a directed fishery in the northern GRA during this study. Thus, had this area been open, limited scup discarding would have occurred. In this study, squid catches averaged 1025 kg tow(-1) in the southern GRA. Thus, had the GRA been open, Loligo fishing would have taken place. Yet, in the 34 tows taken by two vessels, not a single scup was caught. Redeployment of the fleet clearly increased scup discarding in 2003. Thus, Expectation 2 was not met. Field tests demonstrated that the implemented net modification can produce reduced catches of mostly smaller-sized finfish without impairing squid catch, but the data also indicate that this result may not be routinely achieved. Thus, Expectation 3 was not completely met. Implementation of the 2003 net regulation was likely premature, in that the specification was not adequate to guarantee the desired results. The history of the scup discarding issue in the Loligo squid fishery demonstrates that discard reduction cannot be accomplished without adequate prior evaluation of the sources of discards, without the requisite and concomitant experimental evaluation of the results of regulatory reform, and without adequate commercial-scale testing of prospective reforms prior to implementation.     

Trade-off analysis in the Northern Andes to study the dynamics in agricultural land use

In this paper we hypothesize that land use change can be induced by non-linearities and thresholds in production systems that impact farmers' decision making. Tradeoffs between environmental and economic indicators is a useful way to represent dynamic properties of agricultural systems. The Tradeoff Analysis (TOA) System is software designed to implement the integrated analysis of tradeoffs in agricultural systems. The TOA methodology is based on spatially explicit econometric simulation models linked to spatially referenced bio-physical simulation models to simulate land use and input decisions. The methodology has been applied for the potato-pasture production system in the Ecuadorian Andes. The land use change literature often describes non-linearity in land use change as a result of sudden changes in the political (e.g. new agricultural policies) or environmental setting (e.g. earthquakes). However, less attention has been paid to the non-linearities in production systems and their consequences for land use change. In this paper, we use the TOA system to study agricultural land use dynamics and to find the underlying processes for non-linearities. Results show that the sources of non-linearities are in the properties of bio-physical processes and in the decision making-process of farmers.     

Assessment of manure phosphorus export through turfgrass sod production in Erath County, Texas

A best management practice (BMP) for exporting manure phosphorus (P) in turfgrass sod from the North Bosque River (NBR) watershed in central Texas was assessed using a geographic information system (GIS). The NBR watershed has a mandate to reduce the total annual P load to the NBR by 50% as a result of total maximum daily load regulation. Since dairy waste applications to fields are identified as the major nonpoint source of P to the river, innovative BMPs, such as export of manure P in turfgrass, will be needed to achieve the 50% reduction. However, methods are needed to evaluate the feasibility of these innovative management practices prior to their implementation. A geospatial database of suitable turfgrass production sites was developed for Erath County using GIS. Erath County largely encompasses the upper portion of the NBR watershed. Information from field experiments, production practices, and ground-truthing was used to search, analyze, and verify a geospatial database developed from national and regional sources. The integration and analyses of large databases supports the search by turf producers for sites suitable for turfgrass sod production in Erath County. In addition, GIS enables researchers and regulators to estimate manure P exports and reduced P loading due to implementation of the manure export BMP on a county scale. Under optimal conditions 198,000 kg manure P yr(-1) could be used and 114,840 kg manure P yr(-1) exported from the NBR watershed through implementation of a system using dairy manure to produce turfgrass sod. This is the equivalent of the manure P applied from 10,032 dairy cows yr(-1) and exported from 5808 dairy cows yr(-1). Application of GIS to large-scale planning and decision-making transcends traditional field-scale applications in precision agriculture.     

Dissolved phosphorus retention and release from a coastal plain in-stream wetland

Dissolved phosphorus (DP) can be released from wetlands as a result of flooding or shifts in water column concentrations. Our objectives were to determine the long-term (1460 d) DP retention and release characteristics of an in-stream wetland, and to evaluate how these characteristics respond to flooding, draining, and changes in DP concentrations. The studied in-stream wetland drains an agriculturally intensive subwatershed in the North Carolina Coastal Plain region. The wetland's DP retention and release characteristics were evaluated by measuring inflow and outflow DP concentrations, DP mass balance, and DP movement across the sediment-water column interface. Phosphorus sorption isotherms were measured to determine the sediment's equilibria P concentration (EPCo), and passive samplers were used to measure sediment pore water DP concentrations. Initially, the in-stream wetland was undersized (0.31 ha) and released 1.5 kg of DP. Increasing the in-stream wetland area to 0.67 ha by flooding resulted in more DP retention (28 kg) and low outflow DP concentrations. Draining the in-stream wetland from 0.67 to 0.33 ha caused the release of stored DP (12.1 kg). Shifts both in sediment pore water DP concentrations and sediment EPCo values corroborate the release of stored DP. Reflooding the wetland from 0.33 to 0.85 ha caused additional release of stored DP into the outflowing stream (10.9 kg). We conclude that for a time period, this in-stream wetland did provide DP retention. During other time periods, DP was released due to changes in wetland area, rainfall, and DP concentrations.     

Environmental and Economic Factors Can Increase the Risk of Exotic Species Introductions to the Arctic Region Through Increased Ballast Water Discharge

The effects of global warming can increase the risk of exotic species introductions in eastern Canadian Arctic waters by reducing surface ice cover and allow increased access to commercial vessels. Ballast water discharged by incoming overseas vessels is an important means for introducing species on a global scale. Analyses of air temperatures at Churchill, Manitoba between 1943 and 2002 indicated an increase in mean temperature within the past decade. Churchill is the only major northern port in this region where grain has been exported on a limited basis due to the short navigation season. Economic analyses of grain exported from Canadian and U.S. ports indicated some cost advantages for using northern ports. The Hudson Bay region is vulnerable to increased exotic species introductions because of its southerly location. Current ballast water exchange measures to reduce the risk of introductions may not be effective because most vessels enter the region with ballast, and the ballast exchange zone is located relatively close to coastal areas where the habitat could be favorable for an introduced species to become established. The probability of a large crab species introduced to this region from northern European waters is discussed. The risk of ballast water–related exotic species introduction to this region may be reduced by expanding the types of cargo handled and developing a strong import market. This approach would accommodate an increase in the number of vessels with cargo, and substantially reduce the volume of ballast carried to this region.     

Contrasting effects of manure and compost on soil pH, heavy metal availability and growth of Chenopodium album L. in a soil contaminated by pyritic mine waste

Chenopodium album L. was found to be one of the initial plant species colonising a heavy metal-contaminated site, polluted by pyritic (sulphide-rich) waste from the Aznalcóllar mine spill (South-western Spain). This indicates its importance in the re-vegetation of this soil. In a pot experiment, C. album was sown in soil collected from the contaminated site, either non-amended or amended with cow manure or compost produced from olive leaves and olive mill wastewater, in order to study the effect on heavy metal bioavailability and soil pH. In non-amended and compost-amended soils, soil acidification, probably resulting from oxidation and hydrolysis of sulphide, led to increases in the concentrations of soluble sulphate and plant-available Cu, Zn and Mn in the soil (extractable with 0.1 M CaCl(2)). Under these conditions, shoot growth of C. album was negligible and shoot concentrations of Zn (2,420-5,585 microg g(-1)) and Mn (5,513-8,994 microg g(-1)) were phytotoxic. Manure application greatly increased shoot growth and reduced the shoot concentrations of Cu, Zn, and Mn, and their plant-available concentrations in the soil. These effects appeared to be related to an increase of soil pH, due to an inhibition of sulphide oxidation/hydrolysis, relative to the non-amended soil. For metal sulphides-contaminated soil, liable to acidification, manure application appears to be able to enhance the initial stages of re-vegetation, by species such as C. album.     

A new method for testing the sensitivity of active biomonitoring: an example of its application to a terrestrial moss

For the first time, the concepts of limit of detection and limit of quantification, commonly used in analytical chemistry, are applied to the field of active biomonitoring with terrestrial mosses, using the controls as blanks so that the limits indicate the error associated with the transplant technique. The application of these concepts to data corresponding to Hg concentrations in the surroundings of a chlor-alkali plant and a power plant, makes interpretation of the results easier by providing better spatial and temporal coherence. This procedure may allow improvement in the standardization of active biomonitoring techniques as it is applicable to all kinds of biomonitors. One disadvantage of the application of the limit of detection and limit of quantification is that they only take into account the alpha error, or risk of false positives, and do not take into account the beta error, or risk of false negatives.