Seasonal Production and Biomass of the Seagrass, <Emphasis Type="Italic">Halodule wrightii</Emphasis> Aschers. (Shoal Grass), in a Subtropical Texas Lagoon

A study of Halodule wrightii in a shallow subtropical Texas lagoon was performed to obtain seasonal data on its physiological ecology. Leaf production and biomass dynamics of H. wrightii were intensively monitored along with the underwater light environment at a 1.2-m depth study site over a 21-month period from June 1995 to February 1997. The annual photosynthetically active radiation (PAR) flux of 6,764 mol m⁻² year⁻¹ was more than twice as high as 2,400 mol m⁻² year⁻¹, the minimum annual PAR required for maintenance of growth. As light intensity declined, blade chlorophyll a/b ratios increased suggesting that the plants were photo-adapting. Seasonal trends were evident in shoot growth and biomass. Compared to other Halodule populations in Texas, H. wrightii in LLM displayed slow growth and low biomass, high leaf tissue N content, and low C/N ratio but high N/P ratio of 38 suggesting that the plants were phosphorus-limited.     

Determination of Selenium and Tellurium in Basalt Rock Reference Materials by Isotope Dilution Hydride Generation-Inductively Coupled Plasma-Mass Spectrometry (ID-HG-ICP-MS)

Promising methods have been developed recently for the determination of selenium (Se) and tellurium (Te) in geological materials at ng g⁻¹ and lower levels, using hydride generation-inductively coupled plasma-mass spectrometry. Here we report on a new isotope dilution-hydride generation-inductively coupled plasma-mass spectrometry (ID-HG-ICP-MS) method for the simultaneous determination of Se and Te, which is applied to basalts, and modified compared to previous work. The basalts were attacked and dissolved with hydrofluoric and nitric acid, spiked with enriched isotopes, and passed through a cation exchange column (AG 50-X8 100–200 mesh) to separate the major cations that interfere with Se and Te detection (e.g., Fe). The detection limits of this method were 0.010 ng g⁻¹ for Se and 0.0030 ng g⁻¹ for Te, well below the concentrations of Se and Te expected in basalts. The precision of the method for Se was 12.2 to 15.1% and for Te was 4.6 to 7.2% RSD from replicate analyses of basalt reference samples. The accuracy for Se determinations was 61 to 94% and for Te 28 to 100% of values previously reported in the literature for selected USGS reference materials.     

Characterization of a mud deposit offshore of the Patos Lagoon,southern Brazil

Rapid deposition of mud on the beach along the shoreface of Rio Grande do Sul, Brazil dramatically influences the normal operations in the littoral zone. In the surf zone, fluid and suspended mud opposes water-wave movement and dissipates water-wave energy; on the beach, mud limits trafficability. As part of a multinational, multidisciplinary program to evaluate the influence of mud strength, density and viscosity on water-wave attenuation, sediments were evaluated in situ or collected for evaluation from an area offshore of Cassino Beach, slightly south of the Patos Lagoon mouth. Shear strength of deposited sediments ranged from 0.6 kPa at the seafloor to 3.4 kPa at ∼1 m below the seafloor. Mud sediments were also collected to simulate the in situ response of fluid mud to shear stresses. For this determination, rheological evaluations were made using a strain-controlled Couette viscometer on numerous remixed samples that ranged in density from 1.05 to 1.30 g/cm³. It was determined that this mud is a non-ideal Bingham material in that it has a true initial yield stress as well as a upper Bingham yield stress. Initial yield stress ranged from 0.59 to 2.62 Pa, upper Bingham yield stress ranged from 1.05 to 7.6 Pa. Apparent viscosity ranged from 0.02 to 4.7 Pa s with the highest viscosities occurring between the two yield stresses. Sediment strength in the remixed samples is 2 to 3 orders of magnitude lower than the horizontal shear strength of the sediment bed as determined by shear vane or predicted from penetrometer measurements. This difference is partially due to the fact that rheological evaluations are made on fully remixed sediments, whereas horizontal shear strength is determined within relatively undisturbed sediments. Similar values of viscosity and shear strength are comparable to those determined for mud in other coastal areas where fluid mud deposits occur.     

Transforming management of tropical coastal seas to cope with challenges of the 21st century

Over 1.3 billion people live on tropical coasts, primarily in developing countries. Many depend on adjacent coastal seas for food, and livelihoods. We show how trends in demography and in several local and global anthropogenic stressors are progressively degrading capacity of coastal waters to sustain these people. Far more effective approaches to environmental management are needed if the loss in provision of ecosystem goods and services is to be stemmed. We propose expanded use of marine spatial planning as a framework for more effective, pragmatic management based on ocean zones to accommodate conflicting uses. This would force the holistic, regional-scale reconciliation of food security, livelihoods, and conservation that is needed. Transforming how countries manage coastal resources will require major change in policy and politics, implemented with sufficient flexibility to accommodate societal variations. Achieving this change is a major challenge – one that affects the lives of one fifth of humanity.     

Does use of tropical beaches by tourists and island residents result in damage to fringing coral reefs? A case study in Moorea French Polynesia

Although coral reefs worldwide are subject to increasing global threats, humans also impact coral reefs directly through localized activities such as snorkeling, kayaking and fishing. We investigated five sites on the northern shore of Moorea, French Polynesia, and quantified the number of visitors on the beach and in shallow water. In field surveys, we measured total coral cover and colony sizes of two common genera, Porites and Acropora, a massive and branching morphology, respectively. One site, which hosted over an order of magnitude more people than the other four, had significantly less total coral cover and supported very little branching Acropora. In addition, size frequency distributions of both the branching and massive genera were skewed toward smaller colony sizes at the high use site. Our results demonstrated that the use of tropical beaches may result in less coral cover, with branching colonies rare and small.     

Climate Change Impacts for the Conterminous USA: An Integrated Assessment

Human activities have altered the distribution and quality of terrestrial ecosystems. Future demands for goods and services from terrestrial ecosystems will occur in a world experiencing human-induced climate change. In this study, we characterize the range in response of unmanaged ecosystems in the conterminous U.S. to 12 climate change scenarios. We obtained this response by simulating the climatically induced shifts in net primary productivity and geographical distribution of major biomes in the conterminous U.S. with the BIOME 3 model. BIOME 3 captured well the potential distribution of major biomes across the U.S. under baseline (current) climate. BIOME 3 also reproduced the general trends of observed net primary production (NPP) acceptably. The NPP projections were reasonable for forests, but not for grasslands where the simulated values were always greater than those observed. Changes in NPP would be most severe under the BMRC climate change scenario in which severe changes in regional temperatures are projected. Under the UIUC and UIUC + Sulfate scenarios, NPP generally increases, especially in the West where increases in precipitation are projected to be greatest. A CO₂-fertilization effect either amplified increases or alleviated losses in modeled NPP. Changes in NPP were also associated with changes in the geographic distribution of major biomes. Temperate/boreal mixed forests would cover less land in the U.S. under most of the climate change scenarios examined. Conversely, the temperate conifer and temperate deciduous forests would increase in areal extent under the UIUC and UIUC + Sulfate scenarios. The Arid Shrubland/Steppe would spread significantly across the southwest U.S. under the BMRC scenario. A map overlay of the simulated regions that would lose or gain capacity to produce corn and wheat on top of the projected distribution of natural ecosystems under the BMRC and UIUC scenarios (Global mean temperature increase of +2.5 °C, no CO₂ effect) helped identify areas where natural and managed ecosystems could contract or expand. The methods and models employed here are useful in identifying; (a) the range in response of unmanaged ecosystem in the U.S. to climate change and (b) the areas of the country where, for a particular scenario of climate change, land cover changes would be most likely.     

Input of Nutritionally Rich Organic Matter from the Mississippi River to the Louisiana Coastal Zone

Isotopes have often been used to discern riverine subsidies to coastal food chains, but there are few direct measurements of nutritional quality of riverine particulates. We tested for nutritionally enriched organic matter in the Mississippi River suspended sediment and evidence for its delivery to Louisiana coastal sediments by measuring enzymatically hydrolysable amino acids (EHAA). Riverine suspended sediments contained EHAA concentrations of up to 5 mg g^?1, higher than reported in any coastal sediment. Pigment concentrations indicated that EHAA in some river samples were dominated by phytoplankton, but many samples contained significant non-algal EHAA. Coastal sediments showed EHAA concentrations lower than riverine sediments but still higher than most reported shelf values. Incubation of riverine sediment showed losses of 28–34% of their EHAA over 6 days, similar to differences found between riverine and coastal sediments. EHAA concentrations decreased more rapidly than total nitrogen, indicating the relative lability of this pool of material in the studied region. These EHAA-enriched materials provide fuel for various coastal biota whose composition likely depends on factors such as disturbance regimes.     

The environmental tritium concentration of underground water and its hydrological interpretation

Two models which attempt to correlate the tritium concentration of water taken from aquifers to aquifer parameters are discussed. The first takes into account flow along individual streamlines and relates aquifer parameters to the observed tritium concentration at outflow. For the Gambier Plain unconfined aquifer in southern Australia, the calculated tritium concentration at outflow derived from known aquifer parameters and an environmental tritium input function for the area, is 0.7 T.U. The mean tritium concentration of several springs at outflow is also 0.7 T.U.Using the complete mixing model and the approximation that samples withdrawn from an aquifer on Eyre Peninsula, South Australia, are fully mixed, mean annual recharge for the area is estimated at 3 cm/year.     

Sensitivity to climate change of land use and management patterns optimized for efficient mitigation of nutrient pollution

Beginning in the mid-1990s, re-eutrophication has reemerged as severe problems in Lake Erie. Controlling non-point source (NPS) nutrient pollution from cropland, especially dissolved reactive phosphorus (DRP), is the key to restore water quality in Lake Erie. To address NPS pollution, previous studies have analyzed the effectiveness of alternative spatially optimal land use and management strategies (represented as agricultural conservation practices (CPs)). However, few studies considered both strategies and have analyzed and compared their sensitivity to expected changes in temperature and precipitation due to climate change and increased greenhouse gas concentrations. In this study, we evaluated impacts of climatic change on the economic efficiency of these strategies for DRP abatement, using an integrated modeling approach that includes a watershed model, an economic valuation component, and a spatial optimization model. A series of climate projections representing relatively high greenhouse gas emission scenarios was developed for the western Lake Erie basin to drive the watershed model. We found that performance of solutions optimized for current climate was degraded significantly under projected future climate conditions. In terms of robustness of individual strategies, CPs alone were more robust to climate change than land use change alone or together with CPs, but relying on CPs alone fails to achieve a high (>?71%) DRP reduction target. A combination of CPs and land use changes was required to achieve policy goals for DRP reductions (targeted at ~?78%). Our results point to the need for future spatial optimization studies and planning to consider adaptive capacity of conservation actions under a changing climate.     

Evaluation of a Movie Theater Advertisement Campaign to Promote Behaviors that Prevent Spread of Aquatic Invasive Species

One of the primary causes of the spread of aquatic invasive species (AIS) is boaters and anglers who move between bodies of water. Engaging with recreational boaters and anglers to encourage preventative behaviors is crucial for managing the spread of AIS. The use of cinema advertising for disseminating pro-environmental messages is a relatively novel and understudied outreach strategy. To explore this approach, an AIS-related public service announcement was placed in the preshow advertising at a movie theater in north central Wisconsin. Movie patrons were surveyed as they left the theater to determine demographic, AIS awareness, advertising exposure, and recall information. The results of this study suggest movie theater advertising is a potentially efficacious medium for pro-environmental outreach efforts.