Benthic Algal (Periphyton) Growth Rates in Response to Nitrogen and Phosphorus: Parameter Estimation for Water Quality Models

Nitrogen (N) and phosphorus (P) are significant pollutants that can stimulate nuisance blooms of algae. Water quality models (e.g., Water Quality Simulation Program, CE‐QUAL‐R1, CE‐QUAL‐ICM, QUAL2k) are valuable and widely used management tools for algal accrual due to excess nutrients in the presence of other limiting factors. These models utilize the Monod and Droop equations to associate algal growth rate with dissolved nutrient concentration and intracellular nutrient content. Having accurate parameter values is essential to model performance; however, published values for model parameterization are limited, particularly for benthic (periphyton) algae. We conducted a 10‐day mesocosm experiment and measured diatom‐dominated periphyton biomass accrual through time as chlorophyll a (chl a) and ash‐free dry mass (AFDM) in response to additions of N (range 5–11,995 µg nitrate as nitrogen [NO₃‐N]/L) and P (range 0.89–59.51 µg soluble reactive phosphorus/L). Resulting half‐saturation coefficients and growth rates are similar to other published values, but minimum nutrient quotas are higher than those previously reported. Saturation concentration for N ranged from 150 to 2,450 µg NO₃‐N/L based on chl a and from 8.5 to 60 µg NO₃‐N/L when based on AFDM. Similarly, the saturation concentration for P ranged from 12 to 29 µg‐P/L based on chl a, and from 2.5 to 6.1 µg‐P/L based on AFDM. These saturation concentrations provide an upper limit for streams where diatom growth can be expected to respond to nutrient levels and a benchmark for reducing nutrient concentrations to a point where benthic algal growth will be limited.     

Hydrological,Physical, and Chemical Functions and Connectivity of Non‐Floodplain Wetlands to Downstream Waters: A Review

We reviewed the scientific literature on non‐floodplain wetlands (NFWs), freshwater wetlands typically located distal to riparian and floodplain systems, to determine hydrological, physical, and chemical functioning and stream and river network connectivity. We assayed the literature for source, sink, lag, and transformation functions, as well as factors affecting connectivity. We determined NFWs are important landscape components, hydrologically, physically, and chemically affecting downstream aquatic systems. NFWs are hydrologic and chemical sources for other waters, hydrologically connecting across long distances and contributing compounds such as methylated mercury and dissolved organic matter. NFWs reduced flood peaks and maintained baseflows in stream and river networks through hydrologic lag and sink functions, and sequestered or assimilated substantial nutrient inputs through chemical sink and transformative functions. Landscape‐scale connectivity of NFWs affects water and material fluxes to downstream river networks, substantially modifying the characteristics and function of downstream waters. Many factors determine the effects of NFW hydrological, physical, and chemical functions on downstream systems, and additional research quantifying these factors and impacts is warranted. We conclude NFWs are hydrologically, chemically, and physically interconnected with stream and river networks though this connectivity varies in frequency, duration, magnitude, and timing.     

Hydrogeomorphic Reference Condition and Its Relationship with Macroinvertebrate Assemblages in Southeastern U.S. Sand Hills Streams

Defining stream reference conditions is integral to providing benchmarks to ecological perturbation. We quantified channel geometry, hydrologic and environmental variables, and macroinvertebrates in 62 low‐gradient, SE United States (U.S.) Sand Hills (Level IV ecoregion) sand‐bed streams. To identify hydrogeomorphic reference condition (HGM), we clustered channel geometry deviation from expectations given watershed area (Aws), resulting in two HGM groups discriminated by area at the top of bank (Atob) residuals <0.6 m² and >0.6 m² predicted to be HGM reference/nonreference streams, respectively. Two independent partial least squares discriminate analyses used (1) hydrologic/environmental variables and (2) macroinvertebrate mean trait values (mT) on 10 reference/nonreference stream pairs of similar Aws for classification validation. Nonreference streams had flashier hydrographs and altered flow magnitudes, lower organic matter, coarser substrate, higher pH/specific conductivity compared with reference streams. Macroinvertebrate assemblages corresponded to HGM groupings, with mT indicative of multivoltinism, collector‐gatherer functional feeding groups, fast current‐preference taxa, and lower Ephemeroptera, Plecoptera, and Trichoptera richness and biotic integrity in nonreference streams. HGM classifications in Sand Hills, sand‐bed streams were determined from channel geometry. This easily implemented classification is indicative of contemporary hydrologic disturbance resulting in contrasting macroinvertebrate assemblages.     

The need for flexibility in freshwater treaty regimes

Shrinking freshwater supplies pose particular threats in international drainage basins, which serve some 40% of the global population and account for around 60% of the world's river flows. The use and management of these basins are increasingly governed by treaties between the riparian states. While the rules of international law, properly understood, are sufficiently flexible to permit adaptation to changing conditions such as development, population growth and climate change, treaties are essentially rigid instruments that are modifiable only under certain limited conditions. Countries should take this fact into account in designing the regimes to govern their shared freshwater resources, including joint management institutions.     

REEXAMINING BEST MANAGEMENT PRACTICES FOR IMPROVING WATER QUALITY IN URBAN WATERSHEDS1

ABSTRACT: Municipalities will be implementing structural best management practices at increasing rates in their effort to comply with Phase II of the National Pollutant Discharge Elimination System (NPDES). However, there is evidence that structural best management practices (BMPs) by themselves may be insufficient to attain desired water quality standards. This paper reports on an analysis of the median removal efficiencies of structural BMPs and compares them to removal efficiencies estimated as being necessary to attain water quality standards in the Rouge River in Detroit, Michigan. Eight water quality parameters are reviewed using data collected from 1994 to 1999 in the Rouge River. Currently, five of the eight parameters in the Rouge River including bacteria, biochemical oxygen demand, and total suspended solids (TSS) exceed the required water quality standards. The reported analysis of structural BMP efficiencies reveals that structural BMPs appear capable of reducing only some of the pollutants of concern to acceptable levels.     

Stable isotopes provide new insights into vestimentiferan physiological ecology at Gulf of Mexico cold seeps

On the otherwise low-biomass seafloor of the Gulf of Mexico (GoM) continental slope, natural oil and gas seeps are oases of local primary production that support lush animal communities. Hundreds of seep communities have been documented on the continental slope, and nutrition derived from seeps could be an important link in the overall GoM food web. Here, we present a uniquely large and cohesive data set of δ(13)C, δ(15)N, and δ(34)S compositions of the vestimentiferan tubeworms Escarpia laminata and Lamellibrachia sp. 1, which dominate biomass at GoM seeps and provide habitat for hundreds of other species. Our sampling design encompassed an entire region of the GoM lower slope, allowing us for the first time to assess spatial variability in isotope compositions and to robustly address long-standing hypotheses about how vestimentiferans acquire and cycle nutrients over their long lifespan (200+?years). Tissue δ(13)C values provided strong evidence that larger adult vestimentiferans use their buried roots to take up dissolved inorganic carbon from sediment pore water, while very small individuals use their plume to take up carbon dioxide from the seawater. δ(34)S values were extremely variable among individuals of the same species within one location (<1?m(2) area), indicating high variability in the inorganic sulfur pools on a very small spatial scale. This finding supports the hypothesis that vestimentiferans use their roots to cycle sulfate and sulfide between their symbionts and free-living consortia of sulfate-reducing archaea in the sediment. Finally, consistent differences in δ(15)N between two cooccurring vestimentiferan species provided the first strong evidence for partitioning of inorganic resources, which has significant implications for the ecology and evolution of this taxonomic group.     

Using social network analysis tools in ecology: Markov process transition models applied to the seasonal trophic network dynamics of the Chesapeake Bay

Ecosystem components interact in complex ways and change over time due to a variety of both internal and external influences (climate change, season cycles, human impacts). Such processes need to be modeled dynamically using appropriate statistical methods for assessing change in network structure. Here we use visualizations and statistical models of network dynamics to understand seasonal changes in the trophic network model described by Baird and Ulanowicz [Baird, D., Ulanowicz, R.E., 1989. Seasonal dynamics of the Chesapeake Bay ecosystem. Ecol. Monogr. 501 (59), 329–364] for the Chesapeake Bay (USA). Visualizations of carbon flow networks were created for each season by using a network graphic analysis tool (NETDRAW). The structural relations of the pelagic and benthic compartments (nodes) in each seasonal network were displayed in a two-dimensional space using spring-embedder analyses with nodes color-coded for habitat associations (benthic or pelagic). The most complex network was summer, when pelagic species such as sea nettles, larval fishes, and carnivorous fishes immigrate into Chesapeake Bay and consume prey largely from the plankton and to some extent the benthos. Winter was the simplest of the seasonal networks, and exhibited the highest ascendency, with fewest nodes present and with most of the flows shifting to the benthic bacteria and sediment POC compartments. This shift in system complexity corresponds with a shift from a pelagic- to benthic-dominated system over the seasonal cycle, suggesting that winter is a mostly closed system, relying on internal cycling rather than external input. Network visualization tools are useful in assessing temporal and spatial changes in food web networks, which can be explored for patterns that can be tested using statistical approaches. A simulation-based continuous-time Markov Chain model called SIENA was used to determine the dynamic structural changes in the trophic network across phases of the annual cycle in a statistical as opposed to a visual assessment. There was a significant decrease in outdegree (prey nodes with reduced link density) and an increase in the number of transitive triples (a triad in which i chooses j and h, and j also chooses h, mostly connected via the non-living detritus nodes in position i), suggesting the Chesapeake Bay is a simpler, but structurally more efficient, ecosystem in the winter than in the summer. As in the visual analysis, this shift in system complexity corresponds with a shift from a pelagic to a more benthic-dominated system from summer to winter. Both the SIENA model and the visualization in NETDRAW support the conclusions of Baird and Ulanowicz [Baird, D., Ulanowicz, R.E., 1989. Seasonal dynamics of the Chesapeake Bay ecosystem. Ecol. Monogr. 501 (59), 329–364] that there was an increase in the Chesapeake Bay ecosystem's ascendancy in the winter. We explain such reduced complexity in winter as a system response to lowered temperature and decreased solar energy input, which causes a decline in the production of new carbon, forcing nodes to go extinct; this causes a change in the structure of the system, making it simpler and more efficient than in summer. It appears that the seasonal dynamics of the trophic structure of Chesapeake Bay can be modeled effectively using the SIENA statistical model for network change.     

Putting free-riding to work: A Partnership Solution to the common-property problem

The common-property problem results in excessive mining, hunting, and extraction of oil and water. The same phenomenon is also responsible for excessive investment in R&D and excessive outlays in rent-seeking contests. We propose a “Partnership Solution” to eliminate or at least mitigate these excesses. Each of N players joins a partnership in the first stage and chooses his effort in the second stage. Under the rules of a partnership, each member must pay his own cost of effort but receives an equal share of the partnership's revenue. The incentive to free-ride created by such partnerships turns out to be beneficial since it naturally offsets the excessive effort inherent in such problems. In our two-stage game, this institutional arrangement can, under specified circumstances, induce the social optimum in a subgame-perfect equilibrium: no one has a unilateral incentive (1) to switch to another partnership (or create a new partnership) in the first stage or (2) to deviate from socially optimal actions in the second stage. The game may have other subgame-perfect equilibria, but the one associated with the “Partnership Solution” is strictly preferred by every player. We also propose a modification of the first stage which generates a unique subgame-perfect equilibrium. Antitrust authorities should recognize that partnerships can have a less benign use. By organizing as competing partnerships, an industry can reduce the “excessive” output of Cournot oligopoly to the monopoly level. Since no partner has any incentive to overproduce in the current period, there is no need to deter cheating with threats of future punishments.     

Synergistic interactions between edge and area effects in a heavily fragmented landscape

Both area and edge effects have a strong influence on ecological processes in fragmented landscapes, but there is little understanding of how these two factors might interact to exacerbate local species declines. To test for synergistic interactions between area and edge effects, we sampled a diverse beetle community in a heavily fragmented landscape in New Zealand. More than 35,000 beetles of approximately 900 species were sampled over large gradients in habitat area (10(-2) 10(6) ha) and distance from patch edge (2(0)-2(10) m from the forest edge into both the forest and adjacent matrix). Using a new approach to partition variance following an ordination analysis, we found that a synergistic interaction between habitat area and distance to edge was a more important determinant of patterns in beetle community composition than direct edge or area effects alone. The strength of edge effects in beetle-species composition increased nonlinearly with increasing fragment area. One important consequence of the synergy is that the slopes of species area (SA) curves constructed from habitat islands depend sensitively on the distance from edge at which sampling is conducted. Surprisingly, we found negative SA curves for communities sampled at intermediate distances from habitat edges, caused by differential edge responses of matrix- vs. forest-specialist species in fragments of increasing area. Our data indicate that distance to habitat edge has a consistently greater impact on beetle community composition than habitat area and that variation in the strength of edge effects may underlie many patterns that are superficially related to habitat area.