Aeolian dust in Colorado Plateau soils: Nutrient inputs and recent change in source

Aeolian dust (windblown silt and clay) is an important component in arid-land ecosystems because it may contribute to soil formation and furnish essential nutrients. Few geologic surfaces, however, have been characterized with respect to dust-accumulation history and resultant nutrient enrichment. We have developed a combination of methods to identify the presence of aeolian dust in arid regions and to evaluate the roles of this dust in ecosystem processes. Unconsolidated sandy sediment on isolated surfaces in the Canyonlands region of the Colorado Plateau differs greatly in mineralogical and chemical composition from associated bedrock, mainly aeolian sandstone. Detrital magnetite in the surficial deposits produces moderately high values of magnetic susceptibility, but magnetite is absent in nearby bedrock. A component of the surficial deposits must be aeolian to account for the abundance of magnetite, which formed originally in far-distant igneous rocks. Particle-size analysis suggests that the aeolian dust component is typically as much as 20–30%. Dust inputs have enriched the sediments in many elements, including P, Mg, Na, K, and Mo, as well as Ca, at sites where bedrock lacks calcite cement. Soil-surface biologic crusts are effective dust traps that apparently record a change in dust sources over the past several decades. Some of the recently fallen dust may result from human disturbance of land surfaces that are far from the Canyonlands, such as the Mojave Desert. Some land-use practices in the study area have the potential to deplete soil fertility by means of wind-erosion removal of aeolian silt.

Stable isotopes reveal complex changes in trophic relationships following nutrient addition in a coastal marine ecosystem

Complex links between the top-down and bottomup forces that structure communities can be disrupted by anthropogenic alterations of natural habitats.We used relative abundance and stable isotopes to examine changes in epifaunal food webs in seagrass (Thalassia testudinum) beds following 6 months of experimental nutrient addition at two sites in Florida Bay (USA) with different ambient fertility. At a eutrophic site, nutrient addition did not strongly affect food web structure, but at a nutrient-poor site, enrichment increased the abundances of crustacean epiphyte grazers, and the diets of these grazers became more varied. Benthic grazers did not change in abundance but shifted their diet away from green macroalgae + associated epiphytes and towards an opportunistic seagrass (Halodule wrightii) that occurred only in nutrient addition treatments. Benthic predators did not change in abundance, but their diets were more varied in enriched plots. Food chain length was short and unaffected by site or nutrient treatment, but increased food web complexity in enriched plots was suggested by increasingly mixed diets. Strong bottom-up modifications of food web structure in the nutrient-limited site and the limited top-down influences of grazers on seagrass epiphyte biomass suggest that, in this system, the bottom-up role of nutrient enrichment can have substantial impacts on community structure, trophic relationships, and, ultimately, the productivity values of the ecosystem.

Nutrient impacts on epifaunal density and species composition in a subtropical seagrass bed

The capacity of epifauna to control algal proliferation following nutrient input depends on responses of both grazers and upper trophic level consumers to enrichment. We examined the responses of Thalassia testudinum (turtle grass) epifaunal assemblages to nutrient enrichment at two sites in Florida Bay with varying levels of phosphorus limitation. We compared epifaunal density, biomass, and species diversity in 2 m2 plots that had either ambient nutrient concentrations or had been enriched with nitrogen and phosphorus for 6 months. At the severely P-limited site, total epifaunal density and biomass were two times higher in enriched than in unenriched plots. Caridean shrimp, grazing isopods, and gammarid amphipods accounted for much of the increase in density; brachyuran crabs, primary predatory fish, and detritivorous sea cucumbers accounted for most of the increase in biomass. At the less P-limited site, total epifaunal density and biomass were not affected by nutrient addition, although there were more caridean shrimp and higher brachyuran crab and pink shrimp biomass in enriched plots. At both sites, some variation in epifaunal density and biomass was explained by features of the macrophyte canopy, such as T. testudinum and Halodule wrightii percent cover, suggesting that enrichment may change the refuge value of the macrophyte canopy for epifauna. Additional variation in epifaunal density and biomass was explained by epiphyte pigment concentrations, suggesting that enrichment may change the microalgal food resources that support grazing epifauna. Increased epifaunal density in enriched plots suggests that grazers may be able to control epiphytic algal proliferation following moderate nutrient input to Florida Bay.

Phosphorus Biogeochemistry and the Impact of Phosphorus Enrichment: Why Is the Everglades so Unique?

The Florida Everglades is extremely oligotrophic and sensitive to small increases in phosphorus (P) concentrations. P enrichment is one of the dominant anthropogenic impacts on the ecosystem and is therefore a main focus of restoration efforts. In this review, we synthesize research on P biogeochemistry and the impact of P enrichment on ecosystem structure and function in the Florida Everglades. There are clear patterns of increased P concentrations and altered structure and processes along nutrient-enrichment gradients in the water, periphyton, soils, macrophytes, and consumers. Periphyton, an assemblage of algae, bacteria, and associated microfauna, is abundant and has a large influence on phosphorus cycling in the Everglades. The oligotrophic Everglades is P-starved, has lower P concentrations and higher nitrogen–phosphorus (N:P) ratios, and has oxidized to only slightly reduced soil profiles compared to other freshwater wetland ecosystems. Possible general causes and indications of P limitation in the Everglades and other wetlands include geology, hydrology, and dominance of oxidative microbial nutrient cycling. The Everglades may be unique with respect to P biogeochemistry because of the multiple causes of P limitation and the resulting high degree of limitation.

Ocean Acidification Outweighs Nutrient Effects in Structuring Seagrass Epiphyte Communities

Developing a framework for assessing interactions between multiple anthropogenic stressors remains an important goal in environmental research. In coastal ecosystems, the relative effects of aspects of global climate change (e.g. CO2 concentrations) and localized stressors (e.g. eutrophication), in combination, have received limited attention. Using a long-term (11 month) field experiment, we examine how epiphyte assemblages in a tropical seagrass meadow respond to factorial manipulations of dissolved carbon dioxide (CO2(aq)) and nutrient enrichment. In situ CO2(aq) manipulations were conducted using clear, open-top chambers, which replicated carbonate parameter forecasts for the year 2100. Nutrient enrichment consisted of monthly additions of slow-release fertilizer, nitrogen (N) and phosphorus (P), to the sediments at rates equivalent to theoretical maximum rates of anthropogenic loading within the region (1.54 g N m−2 d−1 and 0.24 g P m−2 d−1). Epiphyte community structure was assessed on a seasonal basis and revealed declines in the abundance of coralline algae, along with increases in filamentous algae under elevated CO2(aq). Surprisingly, nutrient enrichment had no effect on epiphyte community structure or overall epiphyte loading. Interactions between CO2(aq) and nutrient enrichment were not detected. Furthermore, CO2(aq)-mediated responses in the epiphyte community displayed strong seasonality, suggesting that climate change studies in variable environments should be conducted over extended time-scales. Synthesis. The observed responses indicate that for certain locations, global stressors such as ocean acidification may take precedence over local eutrophication in altering the community structure of seagrass epiphyte assemblages. Given that nutrient-driven algal overgrowth is commonly cited as a widespread cause of seagrass decline, our findings highlight that alternate climate change forces may exert proximate control over epiphyte community structure.

Boundary Effects on Benthic Microbial Phosphorus Concentrations and Diatom Beta Diversity in a Hydrologically-modified, Nutrient-limited Wetland

Water flow and flooding duration in wetlands influence the structure and productivity of microbial communities partly through their influence on nutrient loading. The effect of flow-regulated nutrient loads is especially relevant for microbial communities in nutrient-poor settings, where delivery controls nutrient uptake rates and the intensity of microbial interactions. We examined the effect of hydrologic history and proximity to water sources on nutrient enrichment of benthic microbial assemblages (periphyton) and on their diatom species composition, along the artificial boundaries of Taylor Slough, a historically phosphorus-depleted drainage of the Florida Everglades. Concentrations of phosphorus in periphyton declined from the wetland boundary near inflow structures to 100-m interior, with spatial and temporal variability in rates dependent on proximity to and magnitude of water flow. Phosphorus availability influenced the beta diversity of diatom assemblages, with higher values near inflow structures where resources were greatest, while interior sites and reference transects contained assemblages with constant composition of taxa considered endemic to the Everglades. This research shows how hydrologic restoration may have unintended consequences when incoming water quality is not regulated, including a replacement of distinctive microbial assemblages by ubiquitous, cosmopolitan ones.

Evidence of Recent Phosphorus Enrichment in Surface Soils of Taylor Slough and Northeast Everglades National Park

Everglades National Park (ENP) is the last hydrologic unit in the series of impounded marsh units that make up the present-day Everglades. The ENP receives water from upstream Water Conservation Areas via canals and water control structures that are highly regulated for flood control, water supply, wildlife management, concerns about poor water quality and the potential for downstream ecosystem degradation. Recent surveys of surface soils in ENP, designed for random sampling for spatial analysis of soil nutrients, did not sample proximate to inflow structures and thus did not detect increased soil phosphorus associated with these water conveyances. This study specifically addressed these areas in a focused sampling effort at three key inflow points in northeast ENP which revealed elevated soil TP proximate to inflows. Two transects extending down Shark River Slough and one down Taylor Slough (a natural watershed of particular ecological value) were found to have soil TP levels in excess of 500 mg kg−1—a threshold above which P enrichment is indicated. These findings suggest the negative impact of elevated water (P) from surface flows and support the assertion that significant soil TP enrichment is occurring in Taylor Slough and other areas of northeastern ENP.

Insulin-like peptide genes in honey bee fat body respond differently to manipulation of social behavioral physiology

Nutrient sensitive insulin-like peptides (ILPs) have profound effects on invertebrate metabolism, nutrient storage, fertility and aging. Many insects transcribe ILPs in specialized neurosecretory cells at changing levels correlated with life history. However, the major site of insect metabolism and nutrient storage is not the brain, but rather the fat body, where functions of ILP expression are rarely studied and poorly understood. Fat body is analogous to mammalian liver and adipose tissue, with nutrient stores that often correlate with behavior. We used the honey bee (Apis mellifera), an insect with complex behavior, to test whether ILP genes in fat body respond to experimentally induced changes of behavioral physiology. Honey bee fat body influences endocrine state and behavior by secreting the yolk protein precursor vitellogenin (Vg), which suppresses lipophilic juvenile hormone and social foraging behavior. In a two-factorial experiment, we used RNA interference (RNAi)-mediated vg gene knockdown and amino acid nutrient enrichment of hemolymph (blood) to perturb this regulatory module. We document factor-specific changes in fat body ilp1 and ilp2 mRNA, the bee`s ILP-encoding genes, and confirm that our protocol affects social behavior. We show that ilp1 and ilp2 are regulated independently and differently and diverge in their specific expression-localization between fat body oenocyte and trophocyte cells. Insect ilp functions may be better understood by broadening research to account for expression in fat body and not only brain.

Managing the Brisbane River and Moreton Bay: an integrated research/management program to reduce impacts on an Australian estuary

The Brisbane River and Moreton Bay Study, an interdisciplinary study of Moreton Bay and its major tributaries, was initiated to address water quality issues which link sewage and diffuse loading with environmental degradation. Runoff and deposition of fine-grained sediments into Moreton Bay, followed by resuspension, have been linked with increased turbidity and significant loss of seagrass habitat. Sewage-derived nutrient enrichment, particularly nitrogen (N), has been linked to algal blooms by sewage plume maps. Blooms of a marine cyanobacterium, Lyngbya majuscula, in Moreton Bay have resulted in significant impacts on human health (e.g., contact dermatitis) and ecological health (e.g., seagrass loss), and the availability of dissolved iron from acid sulfate soil runoff has been hypothesised. The impacts of catchment activities resulting in runoff of sediments, nutrients and dissolved iron on the health of the Moreton Bay waterways are addressed. The Study, established by 6 local councils in association with two state departments in 1994, forms a regional component of a national and state program to achieve ecologically sustainable use of the waterways by protecting and enhancing their health, while maintaining economic and social development. The Study framework illustrates a unique integrated approach to water quality management whereby scientific research, community participation and the strategy development were done in parallel with each other. This collaborative effort resulted in a water quality management strategy which focuses on the integration of socioeconomic and ecological values of the waterways. This work has led to significant cost savings in infrastructure by providing a clear focus on initiatives towards achieving healthy waterways. The Study's Stage 2 initiatives form the basis for this paper.

An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta)

Direct comparisons between photosynthetic O-2 evolution rate and electron transport rate (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing and measured at a depth of 1.8 m, where the midday irradiance rose to 400-600 mumol photons m(-2) s(-1). O-2 exchange was measured with a 5-chamber data-logging apparatus and ETR with a submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((Fm'-Ft)/Fm') decreased from 0.7 during the morning to 0.45 at midday, followed by some recovery in the late afternoon. At low to medium irradiances (0-300 mumol photons m(-2) s(-1)), there was a significant correlation between O-2 evolution and ETR, but at higher irradiances, ETR continued to increase steadily, while O-2 evolution tended towards an asymptote. However at high irradiance levels (600-1200 mumol photons m-(2) s(-1)) ETR was significantly lowered. Two methods of measuring ETR, based on either diel ambient light levels and fluorescence yields or rapid light curves, gave similar results at low to moderate irradiance levels. Nutrient enrichment (increases in [NO3-], [NH4+] and [HPO42-] of 5- to 15-fold over ambient concentrations) resulted in an increase, within hours, in photosynthetic rates measured by both ETR and O-2 evolution techniques. At low irradiances, approximately 6.5 to 8.2 electrons passed through PS II during the evolution of one molecule of O-2, i.e., up to twice the theoretical minimum number of four. However, in nutrient-enriched treatments this ratio dropped to 5.1. The results indicate that PAM fluorescence can be used as a good indication of the photosynthetic rate only at low to medium irradiances.

Assessment of eutrophication status of two Northern Irish Loughs

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia do Ambiente, perfil Engenharia Sanitária

Indicator taxa of benthic diatom communities: a case study in Mediterranean streams

A key issue in the implementation of the Water Framework Directive is the classification of streams and rivers using biological quality parameters and type-specific reference conditions. Four groups of stream types were defined in NE Spain on the basis of 152 diatom samples by means of detrended correspondence analysis and classification techniques. Diatom analysis was restricted to epilithic taxa, and the sites included gradients ranging from near-natural streams to sites with poor ecological quality. The main gradient shows a clear separation of sites in relation to the degree of human influence: polluted streams (mainly located in the lowlands) differ from streams in mountainous areas and in the Pyrenees. A second gradient is related to physiographical features. Headwater streams can be distinguished by their catchment geology. The type-specific diatom taxa for the stream types studied were determined by using indicator species analysis (IndVal). The type-specific taxa from near-natural streams are coincident with the indicator taxa for high ecological status. Human impact reduced the typological heterogeneity of the diatom community composition. Overall, the diatom communities in NE Spain exhibit a regional distribution pattern that closely corresponds with that observed in river systems elsewhere. Physiographical differences are only evident in undisturbed sites, while nutrient enrichment and other human disturbances may mask the regional differences in the distribution of diatom communities

Hydrology, light and the use of organic and inorganic materials as structuring factors of biological communities in Mediterranean streams

Hydrological disturbances, light availability and nutrients are the most relevant factors determining the structure of the biological communities in Mediterranean rivers. While some hydrological disturbances are able to induce catastrophic effects, which may cause a complete reset in physical and biological conditions, continued enrichment or changes in light availability are factors leading to the progressive shift in the communities of autotrophs and heterotrophs in the systems. Primary production in Mediterranean streams shows relevant seasonal changes which mainly follows the variations in light availability. In most forested streams, the algal community is shade-adapted. Nutrient enrichment (especially phosphorus) leads to marked increases in primary production, but this increase is not lineal and there is a saturation of algal biomass even in the most enriched systems. The heterotrophs (bacteria, fungi) are related to the pattern of DOC availability (which most depends on the seasonal discharge and leaf fall dynamics) and to the available substrata in the stream. It has been repeatedly observed that shorttime increases of extracellular enzyme activities are related to the accumulation of autochthonous (algal) and/or allochthonous (leaves) organic matter on the streambed during spring and summer, this being more remarkable in dry than in wetter years. Flow reduction favours detritus concentration in pools, and the subsequent increase in the density and biomass of the macroinvertebrate community. In Mediterranean streams collectors are accounting for the highest density and biomass, this being more remarkable in the least permanent systems, in accordance with the effect of floods on the organic matter availability. Nutrients, through the effect on the primary producers, also affect the trophic food web in the streams by favouring the predominance of grazers

Sedimentação de nutrientes e material particulado em reservatório sob influência de atividades de piscicultura no semiárido do Rio Grande do Norte

Nutrient levels in water reservoirs have been increasing over the years worldwide and fish farming is one of the activities with the potential to cause negative impacts on these environments. Thus, the sedimentation of the main nutrients was evaluated in a reservoir as well as the contribution of aquaculture in raising these rates. The results indicated a significant difference for all nutrients, with higher concentrations in areas near the fish farming, and lower levels in more distant regions. Therefore, assessments that focus only on the water column do not reflect the true impact of this activity.

Distribution and role of macrophytes in coastal lagoons : implications of critical shifts

Crossroads, crucibles and refuges are three words that may describe natural coastal lagoon environments. The words refer to the complex mix of marine and terrestrial influences, prolonged dilution due to the semi-enclosed nature and the function of a habitat for highly diverse plant and animal communities, some of which are endangered. To attain a realistic picture of the present situation, high vulnerability to anthropogenic impact should be added to the description. As the sea floor in coastal lagoons is usually entirely photic, macrophyte primary production is accentuated compared with open sea environments. There is, however, a lack of proper knowledge on the importance of vegetation for the general functioning of coastal lagoon ecosystems. The aim of this thesis is to assess the role of macrophyte diversity, cover and species identity over temporal and spatial scales for lagoon functions, and to determine which steering factors primarily restrict the qualitative and quantitative composition of vegetation in coastal lagoons. The results are linked to patterns of related trophic levels and the indicative potential of vegetation for assessment of general conditions in coastal lagoons is evaluated. This thesis includes five field studies conducted in flads and glo-flads in the brackish water northern Baltic Sea. Flads and glo-flads are defined as a Baltic variety of coastal lagoons, which due to an inlet threshold and post-glacial landuplift slowly will be isolated from the open sea. This process shrinks inlet size, increases exposure and water retention, and is called habitat isolation. The studied coastal lagoons are situated in the archipelago areas of the eastern coast of Sweden, the Åland Islands and the south-west mainland of Finland, where land-uplift amounts to ca. 5 mm/ per year. Out of 400 evaluated sites, a total of 70 lagoons varying in inlet size, archipelago position and anthropogenic influence to cover for essential environmental variation were chosen for further inventory. Vegetation composition, cover and richness were measured together with several hydrographic and morphometric variables in the lagoons both seasonally and inter-annually to cover for general regional, local and temporal patterns influencing lagoon and vegetation development. On smaller species-level scale, the effects of macrophyte species identity and richness for the fish habitat function were studied by examining the influence of plant interaction on juvenile fish diversity. Thus, the active election of plant monoand polycultures by fish and the diversity of fish in the respective culture were examined and related to plant height and water depth. The lagoons and vegetation composition were found to experience a regime shift initiated by increased habitat isolation along with land-uplift. Vegetation composition altered, richness decreased and cover increased forming a less isolated and more isolated regime, named the vascular plant regime and charophyte regime, respectively according to the dominant vegetation. As total phosphorus in the water, turbidity and the impact of regional influences decreased in parallel, the dominance of charophytes and increasing cover seemed to buffer and stabilize conditions in the charophyte regime and indicated an increased functional role of vegetation for the lagoon ecosystem. The regime pattern was unaffected by geographical differences, while strong anthropogenic impact seemed to distort the pattern due to loss of especially Chara tomentosa L. in the charophyte regime. The regimes were further found unperturbed by short-time temporal fluctuations. In fact the seasonal and inter-annual dynamics reinforced the functional difference between the regimes by the increasing role of vegetation along habitat isolation and the resemblance to lake environments for the charophyte regime. For instance, greater total phosphorus and chlorophyll a concentrations in the water in the beginning of the season in the charophyte regime compared with the vascular plant regime presented a steeper reduction to even lower values than in the vascular plant regime along the season. Despite a regional importance and positive relationship of macrophyte diversity in relation to trophic diversity, species identity was underlined in the results of this thesis, especially with decreasing spatial scale. This result was supported partly by the increased role of charophytes in the functioning of the charophyte regime, but even more explicitly by the species-specific preference of juvenile fish for tall macrophyte monocultures. On a smaller species-level scale, tall plant species in monoculture seemed to be able to increase their length, indicating that negative selection forms preferred habitat structures, which increase fish diversity. This negative relationship between plant and fish diversity suggest a shift in diversity patterns among trohic levels on smaller scale. Thus, as diversity patterns seem complex and diverge among spatial scales, it might be ambiguous to extend the understanding of diversity relationships from one trophic level to the other. All together, the regime shift described here presents similarities to the regime development in marine lagoon environments and shallow lakes subjected to nutrient enrichment. However, due to nutrient buffering by vegetation with increased isolation and water retention as a consequence of the inlet threshold, the development seems opposite to the course along an eutrophication gradient described in marine lagoons lacking an inlet threshold, where the role of vegetation decreases. Thus, the results imply devastating consequences of inlet dredging (decreasing isolation) in terms of vegetation loss and nutrient release, and call for increased conservational supervision. Especially the red listed charophytes would suffer negatively from such interference and the consequences are likely to also deteriorate juvenile fish production. The fact that a new species to Finland, Chara connivens Salzm. Ex. Braun 1835 was discovered during this study further indicates a potential of the lagoons serving as refuges for rare species.