Macroinvertebrate community response to eutrophication in an oligotrophic wetland: An in situ mesocosm experiment

Eutrophication from anthropogenic nutrient enrichment is a primary threat to the oligotrophic freshwater marshes of southern Florida. Macrophyte and periphyton response to increased phosphorus (P) has been well documented in both correlative and experimental studies, but the response of consumer communities remains poorly understood, especially in southern marl prairies. We conducted a P-loading experiment in in situ mesocosms in Taylor Slough, Everglades National Park, and examined the response of macroinvertebrate communities. Mesocosms at two sites were loaded weekly with P at four levels: control (0 g P/m2/yr), low (0.2 g P/m2/yr), intermediate (0.8 g P/m2/yr), and high (3.2 g P/m2/ yr). After ∼2 yrs of P-loading, macroinvertebrates were sampled using periphyton mat and benthic floc cores. Densities of macroinvertebrate taxa (no./g AFDM) were two to 16 times higher in periphyton mats than benthic floc. Periphyton biomass decreased with enrichment at one site, and periphyton was absent from many intermediate and all high P treatments at both sites. Total macroinvertebrate density in periphyton mats increased with intermediate P loads, driven primarily by chironomids and nematodes. Conversely, total macroinvertebrate density in benthic floc decreased with enrichment, driven primarily by loss of chironomids and ceratopogonids (Dasyhelea). This study suggests that macroinvertebrate density increases with enrichment until periphyton mats are lost, after which it decreases, and mat infauna fail to move into benthic substrates in response to mat loss. These results were noted at nutrient levels too low to yield anoxia, and we believe that the decrease of macroinvertebrate density resulted from a loss of habitat. This work illustrates the importance of periphyton mats as habitat for macroinvertebrates in the Everglades. This study also indicates that in this system, macroinvertebrate sampling should be designed to target periphyton mats or conducted with special attention to inclusion of substrates relative to their coverage.

Spatiotemporal patterns in community structure of macroinvertebrates inhabiting calcareous periphyton mats

Calcareous floating periphyton mats in the southern Everglades provide habitat for a diverse macroinvertebrate community that has not been well characterized. Our study described this community in an oligotrophic marsh, compared it with the macroinvertebrate community associated with adjacent epiphytic algae attached to macrophytes in the water column, and detected spatial patterns in density and community structure. The floating periphyton mat (floating mat) and epiphytic algae in the water column (submerged epiphyton) were sampled at 4 sites (1 km apart) in northern Shark River Slough, Everglades National Park (ENP), in the early (July) and late (November) wet season. Two perpendicular 90-m transects were established at each site and 100 samples were taken in a nested design. Sites were located in wet-prairie spikerush-dominated sloughs with similar water depths and emergent macrophyte communities. Floating mats were sampled by taking cores (6-cm diameter) that were sorted under magnification to enumerate infauna retained on a 250-μm-mesh sieve and with a maximum dimension >1 mm. Our results showed that floating mats provide habitat for a macroinvertebrate community with higher densities (no. animals/g ash-free dry mass) of Hyalella azteca, Dasyhelea spp., and Cladocera, and lower densities of Chironomidae and Planorbella spp. than communities associated with submerged epiphyton. Densities of the most common taxa increased 3× to 15× from early to late wet season, and community differences between the 2 habitat types became more pronounced. Floating-mat coverage and estimated floating-mat biomass increased 20 to 30% and 30 to 110%, respectively, at most sites in the late wet season. Some intersite variation was observed in individual taxa, but no consistent spatial pattern in any taxon was detected at any scale (from 0.2 m to 3 km). Floating mats and their resident macroinvertebrate communities are important components in the Everglades food web. This community should be included in environmental monitoring programs because degradation and eventual loss of the calcareous periphyton mat is associated with P enrichment in this ecosystem.

Phosphorus budgets in Everglades wetland ecosystems: the effects of hydrology and nutrient enrichment

The Florida Everglades is a naturally oligotrophic hydroscape that has experienced large changes in ecosystem structure and function as the result of increased anthropogenic phosphorus (P) loading and hydrologic changes. We present whole-ecosystem models of P cycling for Everglades wetlands with differing hydrology and P enrichment with the goal of synthesizing existing information into ecosystem P budgets. Budgets were developed for deeper water oligotrophic wet prairie/slough (‘Slough’), shallower water oligotrophic Cladium jamaicense (‘Cladium’), partially enriched C. jamaicense/Typha spp. mixture (‘Cladium/Typha’), and enriched Typha spp. (‘Typha’) marshes. The majority of ecosystem P was stored in the soil in all four ecosystem types, with the flocculent detrital organic matter (floc) layer at the bottom of the water column storing the next largest proportion of ecosystem P pools. However, most P cycling involved ecosystem components in the water column (periphyton, floc, and consumers) in deeper water, oligotrophic Slough marsh. Fluxes of P associated with macrophytes were more important in the shallower water, oligotrophic Cladium marsh. The two oligotrophic ecosystem types had similar total ecosystem P stocks and cycling rates, and low rates of P cycling associated with soils. Phosphorus flux rates cannot be estimated for ecosystem components residing in the water column in Cladium/Typha or Typha marshes due to insufficient data. Enrichment caused a large increase in the importance of macrophytes to P cycling in Everglades wetlands. The flux of P from soil to the water column, via roots to live aboveground tissues to macrophyte detritus, increased from 0.03 and 0.2 g P m−2 yr−1 in oligotrophic Slough and Cladium marsh, respectively, to 1.1 g P m−2 yr−1 in partially enriched Cladium/Typha, and 1.6 g P m−2 yr−1 in enriched Typha marsh. This macrophyte translocation P flux represents a large source of internal eutrophication to surface waters in P-enriched areas of the Everglades.

Seasonal differences in the CO2 exchange of a short-hydroperiod Florida Everglades marsh

Although wetlands are among the world's most productive ecosystems, little is known of long-term CO2 exchange in tropical and subtropical wetlands. The Everglades is a highly managed wetlands complex occupying >6000 km2 in south Florida. This ecosystem is oligotrophic, but extremely high rates of productivity have been previously reported. To evaluate CO2 exchange and its response to seasonality (dry vs. wet season) in the Everglades, an eddy covariance tower was established in a short-hydroperiod marl marsh. Rates of net ecosystem exchange and ecosystem respiration were small year-round and declined in the wet season relative to the dry season. Inundation reduced macrophyte CO2 uptake, substantially limiting gross ecosystem production. While light and air temperature exerted the primary controls on net ecosystem exchange and ecosystem respiration in the dry season, inundation weakened these relationships. The ecosystem shifted from a CO2 sink in the dry season to a CO2 source in the wet season; however, the marsh was a small carbon sink on an annual basis. Net ecosystem production, ecosystem respiration, and gross ecosystem production were −49.9, 446.1 and 496.0 g C m−2 year−1, respectively. Unexpectedly low CO2 flux rates and annual production distinguish the Everglades from many other wetlands. Nonetheless, impending changes in water management are likely to alter the CO2 balance of this wetland and may increase the source strength of these extensive short-hydroperiod wetlands.

Historic primary producer communities linked to water quality and hydrologic changes in the northern Everglades

The northern Everglades Water Conservation Areas have experienced recent ecological shifts in primary producer community structure involving marl periphyton mats and dense Typha-dominated macrophyte stands. Multiple investigations have identified phosphorus (P) as a driver of primary producer community structure, but effects of water impoundment beginning in the 1950s and changes in water hardness [e.g., (CaCO3)] have also been identified as a concern. In an effort to understand pre-1950, primary producer community structure and identify community shifts since 1950, we measured pigment proxies on three sediment cores collected in Water Conservation Area-2A (WCA-2A) along a phosphorus enrichment gradient. Photosynthetic pigments, sediment total phosphorus content (TP), organic matter, total organic carbon and nitrogen were used to infer historic primary producer communities and changes in water quality and hydrology regulating those communities. Excess 210Pb was used to establish historic dates for the sediment cores. Results indicate the northern area of WCA-2A increased marl deposition and increased algal abundance ca. 1920. This increase in (presumably) calcareous periphyton before intensive agriculture and impoundment suggest canal-derived calcium inputs and to some extent early drainage effects played a role in initiating this community shift. The northern area community then shifted to Typha dominance around 1965. The areas to the south in WCA-2A experienced increased marl deposition and algal abundance around or just prior to 1950s impoundment, the precise timing limited by core age resolution. Continued increases in algal abundance were evident after 1950, coinciding with impoundment and deepening of canals draining into WCA-2A, both likely increasing water mineral and nutrient concentrations. The intermediate site developed a Typha-dominated community ca. 1995 while the southern-most core site WCA-2A has yet to develop Typha dominance. Numerous studies link sediment TP >650 mg P/kg to marsh habitat degradation into Typha-dominance. The northern and intermediate cores where Typha is currently support this previous research by showing a distinct shift in the sediment record to Typha dominance corresponding to sediment TP between 600 and 700 mg P/kg. These temporal and spatial differences are consistent with modern evidence showing water-column gradients in mineral inputs (including Ca, carbonates, and phosphorus) altering primary producer community structure in WCA-2A, but also suggest hydroperiod has an effect on the mechanisms regulating periphyton development and Typha dominance.

Ecosystem structure in disturbed and restored subtropical seagrass meadows

Shallow seagrass ecosystems frequently experience physical disturbance from vessel groundings. Specific restoration methods that modify physical, chemical, and biological aspects of disturbances are used to accelerate recovery. This study evaluated loss and recovery of ecosystem structure in disturbed seagrass meadows through plant and soil properties used as proxies for primary and secondary production, habitat quality, benthic metabolism, remineralization, and nutrient storage and exchange. The efficacy of common seagrass restoration techniques in accelerating recovery was also assessed. Beyond removal of macrophyte biomass, disturbance to seagrass sediments resulted in loss of organic matter and stored nutrients, and altered microbial and infaunal communities. Evidence of the effectiveness of restoration actions was variable. Fill placement prevented additional erosion, but the resulting sediment matrix had different physical properties, low organic matter content and nutrient pools, reduced benthic metabolism, and less primary and secondary production relative to the undisturbed ecosystem. Fertilization was effective in increasing nitrogen and phosphorus availability in the sediments, but concurrent enhancement of seagrass production was not detected. Seagrass herbivores removed substantial seagrass biomass via direct grazing, suggesting that leaf loss to seagrass herbivores is a spatially variable but critically important determinant of seagrass transplanting success. Convergence of plant and sediment response variables with levels in undisturbed seagrass meadows was not detected via natural recovery of disturbed sites, or through filling and fertilizing restoration sites. However, several indicators of ecosystem development related to primary production and nutrient accumulation suggest that early stages of ecosystem development have begun at these sites. This research suggests that vessel grounding disturbances in seagrass ecosystems create more complex and persistent resource losses than previously understood by resource managers. While the mechanics of implementing common seagrass restoration actions have been successfully developed by the restoration community, expectations of consistent or rapid recovery trajectories following restoration remain elusive.

Left to right: Laura and Damon collecting periphyton at TS/Ph-2, Taylor Slough

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. This image is made available for non-commercial or educational use only.

Assessing the Legacy of Red Mud Pollution in a Shallow Freshwater Lake: Arsenic Accumulation and Speciation in Macrophytes

Little is known about long-term ecological responses in lakes following red mud pollution. Among red mud contaminants, arsenic (As) is of considerable concern. Determination of the species of As accumulated in aquatic organisms provides important information about the biogeochemical cycling of the element and transfer through the aquatic food-web to higher organisms. We used coupled ion chromatography and inductively coupled plasma mass spectrometry (ICP-MS) to assess As speciation in tissues of five macrophyte taxa in Kinghorn Loch, UK, 30 years following the diversion of red mud pollution from the lake. Toxic inorganic As was the dominant species in the studied macrophytes, with As species concentrations varying with macrophyte taxon and tissue type. The highest As content measured in roots of Persicaria amphibia (L.) Gray (87.2 mg kg-1) greatly exceeded the 3 - 10 mg kg-1 range suggested as a potential phytotoxic level. Accumulation of toxic As species by plants suggested toxicological risk to higher organisms known to utilise macrophytes as a food source.

Environmental impacts of freshwater use and suspended solids in life cycle assessment

Perturbation of natural ecosystems, namely by increasing freshwater use and its degradative use, as well as topsoil erosion by water of land-use production systems, have been emerging as topics of high environmental concern. Freshwater use has become a focus of attention in the last few years for all stakeholders involved in the production of goods, mainly agro-industrial and forest-based products, which are freshwater-intensive consumers, requiring large inputs of green and blue water. This thesis presents a global review on the available Water Footprint Assessment and Life Cycle Assessment (LCA)-based methods for measuring and assessing the environmental relevance of freshwater resources use, based on a life cycle perspective. Using some of the available midpoint LCA-based methods, the freshwater use-related impacts of a Portuguese wine (white ‘vinho verde’) were assessed. However, the relevance of environmental green water has been neglected because of the absence of a comprehensive impact assessment method associated with green water flows. To overcome this constraint, this thesis helps to improve and enhance the LCA-based methods by providing a midpoint and spatially explicit Life Cycle Impact Assessment (LCIA) method for assessing impacts on terrestrial green water flow and addressing reductions in surface blue water production caused by reductions in surface runoff due to land-use production systems. The applicability of the proposed method is illustrated by a case study on Eucalyptus globulus conducted in Portugal, as the growth of short rotation forestry is largely dependent on local precipitation. Topsoil erosion by water has been characterised as one of the most upsetting problems for rivers. Because of this, this thesis also focuses on the ecosystem impacts caused by suspended solids (SS) from topsoil erosion that reach freshwater systems. A framework to conduct a spatially distributed SS delivery to freshwater streams and a fate and effect LCIA method to derive site-specific characterisation factors (CFs) for endpoint damage on aquatic ecosystem diversity, namely on algae, macrophyte, and macroinvertebrates organisms, were developed. The applicability of this framework, combined with the derived site-specific CFs, is shown by conducting a case study on E. globulus stands located in Portugal as an example of a land use based system. A spatially explicit LCA assessment was shown to be necessary, since the impacts associated with both green water flows and SS vary greatly as a function of spatial location.

Invertebrate communities of Nabugabo Lakes: a vital support resource for the fisheries and ecosystem diversity

A field study of the invertebrate communities of the Nabugabo lakes(Nabugabo,Kayanja and Kayugi)showed the occurrence of copepoda, cladocera and rotifera(micro-invertebrates or zooplankton); Ephemeroptera and Diptera(macro-invertebrates or zoo-benthos). The most commonly encountered taxa were thermocyclops neglectus, moinamicrura,several rotiferan species(micro-invertebrates);P.adusta,chironomus, tanipodinae and trichoptera(macro- invertebrates). These organisms are assumed to be readily available as food sources for fishes in the Nabugabo lakes. Higher abundance and diversity of invertebrates occurred in Lake Nabugabo compared to Kayanja and Kayugi. There were no major differences in diversity and abundance of organisms between inshore and offshore areas of the different lakes. The highest diversity of macro-invertebrates(up to 15 taxa)was recovered from roots of macrophyte(higher water-based plants)such as Miscanthidium and Papyrus. The zooplankton of Nabugabo lakes typify a tropical assemblage with few species among genera and dominance of the communities by small-bodied organisms. Some taxa,common to many other water bodies such as Mesocyclops spp.,Calanoids(Copepoda), Caridina nilotica (Decapoda)were noticeably missing in the Nabugabo lakes community, probably due to environmental limitations including low conductivity and pH. Where they occur,these missing taxa have been shown to be key forage items for fishes and therefore their absence in Nabugabo lakes may have implications with respect to potential for fishery production. However other valuable invertebrate types such as cyclopoid copepods,ephemeroptera, chironomid and chaoborid larvae do occur in sufficiently high diversity and abundance to support viable fisheries resources. The high diversity and abundance of invertebrates associated with aquatic macrophytes such as Papyrus and Miscanthidium need to be protected through control of access and utilisation of shoreline vegetation.

Nabugabo lakes and their current conservation status

Fish species diversity in Lake Nabugabo, Uganda, has declined following establishment of the introduced fish species in the lake. Most of the native fish species have disappeared and the lake is now dominated by the introduced Nile perch, Lates niloticus and the Nile tilapia Oreochromis niloticus. The dominant native fish species include Synodontis afrofischeri, Schilbe intermedius, Rastrineobola argentea and Brycinussadleri. Some of the native fish species that have disappeared from Lake Nabugabo were reported to occur in lakes Kayugi and Kayanja, which are adjacent to Lake Nabugabo but separated from it by extensive papyrus swamps. The Nabugabo lakes are satellite water bodies in the Lake Victoria basin, which is known to have experienced fish species changes due to the introduction of the Nile perch Lates niloticus during the 1960s.The Nabugabo lakes comprising of Lake Nabugabo main, and the smaller lakes Kayanja and Kayugi were investigated between 2000 and 2002 with experimental gill netting to evaluate the potential of these lakes in conservation of fish species diversity. Results show that some native fish species especially Oreochromis esculentus, and Oreochromis variabilis and the haplochromine cichlid Prognathochromis venator that have disappeared from Lake Nabugabo still occur in Lakes Kayanja and Kayugi. Inshore habitats with macrophyte cover were also found to be important habitats for the endangered native fish species in the Nabugabo lakes. These lakes and inshore habitats need to be protected to conserve the endangered native fish species and to reduce further decline in fish species diversity.

Satellite lakes as reservoirs of fish species diversity

Satellite lakes and rivers in the Victoria and Kyoga basins provide a sanctuary for endangered native fish species. The structural heterogeneity of macrophyte covering these lakes has made it possible for most of the biodiversity to be kept intact. The Kyoga minor lakes have the highest fish species diversity especially of the haplochromines. Most fish communities of these satellite lakes are composed of native species.

A boat hitchhiker's guide to survival: Cabomba caroliniana desiccation resistance and survival ability

Cabomba caroliniana is a submersed macrophyte that has become a serious invader. Cabomba predominantly spreads by stem fragments, in particular through unintentional transport on boat trailers ('hitch hiking'). Desiccation resistance affects the potential dispersal radius. Therefore, knowledge of maximum survival times allows predicting future dispersal. Experiments were conducted to assess desiccation resistance and survival ability of cabomba fragments under various environmental scenarios. Cabomba fragments were highly tolerant of desiccation. However, even relatively low wind speeds resulted in rapid mass loss, indicating a low survival rate of fragments exposed to air currents, such as fragments transported on a boat trailer. The experiments indicated that cabomba could survive at least 3 h of overland transport if exposed to wind. However, even small clumps of cabomba could potentially survive up to 42 h. Thus, targeting the transport of clumps of macrophytes should receive high priority in management. The high resilience of cabomba to desiccation demonstrates the risk of continuing spread. Because of the high probability of fragment viability on arrival, preventing fragment uptake on boat trailers is paramount to reduce the risk of further spread. These findings will assist improving models that predict the spread of aquatic invasive macrophytes.

Efeitos do cobre na macrófita potamogeton pectinatus L. e sua possível utilização o monitoramento ou remediação de ambientes aquáticos contaminados por este metal

O cobre é um metal essencial para as plantas, porém considerado tóxico quando em elevadas concentrações na água. No caso de macrófitas aquáticas já foi demonstrado que este metal inibe o processo fotossintético e provoca alterações pigmentares. Neste contexto, expusemos (96h) a macrófita aquática Potamogeton pectinatus (L.) à diferentes concentrações de cobre 1, 10, 100 e 1000 µM para avaliar o potencial bioacumulador da planta, e às concentrações de 1, 10 e 100 µM de Cu para verificar os possíveis efeitos do metal na taxa fotossintética (24 e 96h) em diferentes intensidades luminosas (17, 100, 300 e 500 µmol/m2 /s), no teor pigmentar (96h) e no crescimento das macrófitas (30 dias). Para os experimentos de bioacumulação mantivemos um grupo de plantas controle (sem adição de cobre no meio), enquanto que para os outros testes mantivemos um grupo controle e um grupo em solução nutritiva de Hoagland 100%, que contem cobre e outros micronutrientes em concentrações ideais para sobrevivência e crescimento de P. pectinatus. Nossos resultados mostram que a macrófita P. pectinatus é capaz de acumular altas concentrações de cobre, sendo que este acúmulo aumenta com a elevação dos níveis do metal na água. Apesar de basicamente não haver diferença estatística entre a concentração do metal nos diferentes órgãos da planta, as raízes mostraram-se capazes de acumular mais cobre que as folhas e caule com base no fator de bioconcentração. Com relação aos teores de clorofila “a”, “b” e carotenoides, estes foram menores nas folhas das plantas controle em comparação com as plantas em solução de Hogland, mas esta diferença só foi significativa nas plantas expostas ao cobre, que apresentaram menor concentração dos teores pigmentares já à 1 µM de Cu. Quanto à fotossíntese, em 24h de exposição, novamente observamos um efeito negativo da ausência e presença de cobre nas concentrações de 1, 10 e 100 µM, bem como, um efeito da luminosidade, de forma que as plantas em solução de Hoagland apresentaram maior taxa fotossintética quando em 100 µmol/m2 /s. Em virtude de um aumento na respiração em 96h, a fotossíntese, quando ocorreu, foi menor que em 24h e não diferiu entre os grupos e luminosidade. Em relação ao crescimento, as plantas perderam biomassa, mas mantiveram seus comprimentos e apenas aquelas em solução de Hoagland aumentaram seu número de folhas. Ainda, verificou-se clorose e necrose nas plantas controle e expostas ao cobre. Diante do exposto, concluímos que a macrófita P. pectinatus acumula altas concentrações de cobre, principalmente na raiz, sendo capaz e refletir as concentrações do metal no meio. Esta condição, sugere seu uso no biomonitoramento e fitorremediação de locais contaminados por cobre. Por outro lado, elas mostram-se sensíveis ao metal pela redução no teor pigmentar e fotossíntese, sugerindo estes como mecanismos toxicidade do cobre.

Avaliação do potencial da macrófita Pistia stratiotes na exposição de íon cromo (VI): biossorção e tolerância

The environmental pollution caused by industries has increased the concentration of pollutants in the environment, especially in water. Among the most diverse contaminants, there is the metals, who may or may not to be heavy/toxic, causing effluent of difficult treatment when in low concentrations. The search for alternative measures of wastewater effluent treatment has led to studies using phytoremediation technique through the various matrices (plant, fungi, bacteria) as means of polishing treatment to remove contaminants by means of biosorption/bioaccumulation. In order to use the phytoremediation technique for removing metals of the environmental, it have been performed bioassay with the macrophyte Pistia stratiotes. The bioassays were realized with healthy plants of P. stratiotes acclimatized in a greenhouse, at room temperature and lighting conditions during 28 days of cultivate. The cultivations were performed in glass vessels containing 1 L of the hydroponic solution with chromium (VI) in the potassium dichromate form with concentration range 0.10 to 4.90 mg L-1. The experiments were performed by Outlining Central Composite Rotational (OCCR), where the kinetics of bioaccumulation and chlorophyll a fluorescence were monitored in plants of P. stratiotes during cultivation. The collections of the samples and cultive solution were performed according to the OCCR. The chromium levels were measured in samples of P. stratiotes and the remaining solutions by the methodology of atomic absorption spectrometry by flame. The tolerance of P. stratiotes in relation to exposure to chromium (VI) was analyzed by parameters of physiological activity by means of chlorophyll a fluorescence, using the portable fluorometer PAM (Pulse Amplitude Modulation). The development of P. stratiots and their biomass were related to the time factor, while bioaccumulation capacities were strongly influenced by factors of time and chromium concentration (VI). The chlorophyll fluorescence parameters were affected by chromium and the exposure time at the bioassays. It was obtained an higher metal removal from the root in relation to the sheet, reaching a high rate of metal removal in solution. The experimental data removal kinetics were represented by kinetic models Irreversibly Langmuir, Reversible Langmuir, Pseudo-first Order and Pseudo-second Order, and the best fit for the culture solution was the Reversible Langmuir model with R² 0.993 and for the plant the best model was Pseudo-second order with R² 0.760.