Phosphatase activity as an early warning indicator of wetland eutrophication: problems and prospects

A phosphorus (P) loading experiment conducted in the oligotrophic P-limited Everglades was used to assess the utility of phosphatase activity (PA) of periphyton as an early warning (EW) indicator of wetland eutrophication. Phosphorus loads of 0, 0.4, 0.8, 1.6, 3.2, 6.4 and 12.8 g P m^–2 yr^–1 were applied to mesocosms placed in a slough community consisting of Cladium jamaicense Crantz, Eleocharis spp. and calcareous periphyton mats. Phosphatase activity, expressed on a biomass-specific basis, was not a sensitive indicator of P enrichment for epiphytic periphyton growing on acrylic dowels or floating mat periphyton. However, surface-area-specific PA was a sensitive indicator of P enrichment, responding within 2–3 weeks of the initiation of dosing. Surface-area-specific PA of unenriched periphyton ranged from 0.42 to 0.7 nmol cm^–2 min^–1, while PA of periphyton growing in the highest load (12.8 g P m^–2 yr^–1), ranged from 0.11 to 0.29 nmol cm^–2 min^–1. Conclusions drawn from PA analyses were consistent with those obtained from periphyton primary productivity and P content. Phosphatase activity is a potentially valuable EW indicator when used in conjunction with other complementary indicators.     

Effects of increased phosphorus loading on dissolved oxygen in a subtropical wetland, the Florida Everglades

The Florida Everglades is an oligotrophic, phosphorus (P)-limited wetland that is experiencing eutrophication as a result of P-enriched agricultural runoff. Effects of P enrichment on diel water-column dissolved oxygen concentration (DO) profiles were measured along nutrient gradients downstream of agricultural discharges in two northern Everglades marshes and in field enclosures (mesocosms) exposed to different P loading rates. Reference (i.e., water-column TP < 10 g/L) areas in the marsh interior were characterized by strong diel fluctuations in DO, and aerobic conditions generally were maintained throughout the diel cycle. Enriched stations (water-column TP elevated to between 12 and 131 g/L) were characterized by dampened diel fluctuations and reduced DO, and the extent of these changes was correlated strongly with marsh P concentrations. Mean DO declined from between 1.81 and 7.52 mg/L at reference stations to between 0.04 and 3.18 mg/L in highly enriched areas. Similarly, minimum DO declined from between 0.33 and 5.86 mg/L to between 0 and 0.84 mg/L with increasing enrichment, and the frequency of extremely low DO (< 1 mg/L) increased from between 0 and 20% to as high as 100% in the most enriched areas. Diel oxygen profiles in P-enriched mesocosms declined progressively with time; all loading treatments exhibited similar DO during the 1^st year of P loading, but concentrations declined significantly at higher loads by year 3. Reductions in water-column DO with increased P enrichment were associated with reduced oxygen production by submersed periphyton and macrophytes and increased sediment oxygen demand. Increased emergent macrophyte cover in enriched areas likely contributed to these changes by shading the water-column, which inhibited submerged productivity, and by providing inputs of nutrient-rich detritus, which increased oxygen demand. Declines in marsh DO are associated with other ecological changes such as increased anaerobic metabolism and an increase in invertebrate taxa that tolerate low DO. While background oxygen concentrations in wetlands can be lower than those in lakes and rivers, declines in water-column DO caused by eutrophication can result in biological impacts similar to those in other aquatic ecosystems.     

Periphyton as a potential phosphorus sink in the Everglades Nutrient Removal Project

Phosphorus uptake and release by periphyton mats were quantified in the Everglades Nutrient Removal Project (ENRP) to evaluate the potential for periphyton P removal. Short-term P uptake rates were determined by incubating cyanobacteria (Oscillatoria princeps and Shizothrix calcicola) and Chlorophycean (primarily Rhizoclonium spp.) algal mat samples for 0.5–2 h under ambient conditions in BOD bottles spiked with soluble reactive P (SRP). Cyanobacterial mats removed P more than twice as fast (80–164 μg P h⁻¹ g⁻¹ AFDM) as Chlorophycean mats (33–61 μg P h⁻¹ g⁻¹ AFDM) during these incubations. In a longer term study, fiberglass cylinders were used to enclose 1.8 m² plots within the wetland and were dosed weekly for 7 weeks with: (1) no nutrients; (2) SRP (0.25 g P m⁻² week⁻¹); or (3) SRP plus nitrate (0.42 g N m⁻² week⁻¹) and ammonium (0.83 g N m⁻² week⁻¹). Phosphorus uptake rates by this periphyton assemblage, which was dominated by the chlorophytes Stigeoclonium spp. and Oedogonium spp., were measured weekly and were similar among nutrient treatments on most dates, indicating that the algal storage compartment for P was not saturated despite repeated P additions. Decomposition rates and P loss by cyanobacteria and Chlorophycean mats were determined by measuring biomass loss and SRP release in darkened BOD bottles over 28–42 day periods under anaerobic and aerobic conditions. First-order aerobic and anaerobic decomposition rates for cyanobacterial mats (k = 0.1095 and 0.1408 day⁻¹, respectively) were 4–20-fold higher than rates for Chlorophycean mats (k = 0.0066 and 0.0250 day⁻¹, respectively) and cyanobacteria released considerably more P back to the water column. Our findings suggest that periphyton can be an important short-term sink for P in treatment wetlands and that retention is strongly affected by the taxonomic composition of the periphyton assemblage.     

Effects of nutrients and fish on periphyton and plant biomass across a European latitudinal gradient

Replicated, factorial mesocosm experiments were conducted across Europe to study the effects of nutrient enrichment and fish density on macrophytes and on periphyton chlorophyll a (chl-a) with regard to latitude. Periphyton chl-a densities and plant decline were significantly related to nutrient loading in all countries. Fish effects were significant in a few sites only, mostly because of their contribution to the nutrient pool. A saturation-response type curve in periphyton chl-a with nutrients was found, and northern lakes achieved higher densities than southern lakes. Nutrient concentration and phytoplankton chl-a necessary for a 50% plant reduction followed a latitudinal gradient. Total phosphorus values for 50% plant disappearance were similar from Sweden (0.27 mg L⁻¹) to northern Spain (0.35 mg L⁻¹), but with a sharp increase in southern Spain (0.9 mg L⁻¹). Planktonic chl-a values for 50% plant reduction increased monotonically from Sweden (30 μg L⁻¹) to València (150 μg L⁻¹). Longer plant growing-season, higher light intensities and temperature, and strong water-level fluctuations characteristic of southern latitudes can lead to greater persistence of macrophyte biomass at higher turbidities and nutrient concentration than in northern lakes. Results support the evidence that latitudinal differences in the functioning of shallow lakes should be considered in lake management and conservation policies.     

Association between phosphorus and suspended solids in an Everglades treatment wetland dominated by submersed aquatic vegetation

Restoration of the Everglades requires reduction of total phosphorus (TP) in the influent run-off from the Everglades agricultural area (EAA). The Everglades nutrient removal project tested phosphorus (P) - removal efficiencies of several treatment wetland cells. The best TP reduction has occurred within the submersed aquatic vegetation (SAV) - dominated treatment Cell 4. A significant proportion of the P reduction in Cell 4 over several years has been in the form of particulate P (PP). This study was conducted to (i) determine and compare the components of suspended solids in the Cell 4 influent and effluent waters, and (ii) investigate associations between PP and individual particulate components. Identification and quantification of components were accomplished using X-ray diffraction, thermogravimetry, scanning electron microscopy, and energy dispersive X-ray elemental analysis. The dominant particulate components in the Cell 4 water column are organic matter (OM), biogenic Si (predominantly diatom frustules), and calcite. Concentrations of PP, suspended solids, and particulate OM were greater at the Cell 4 inflow than at the outflow; consistent differences between particulate calcite in the influent vs. the effluent were not found. PP was positively correlated with particulate OM, but was not correlated with calcite. Data suggest that particulate OM, including microbial cells, plays an important role in P transport from the EAA. Possibly, a shift from planktonic to periphytic microbial distribution contributes to PP reduction. The importance of planktonic organisms as vectors of P in Everglades water warrants further study.     

Catabolic diversity of periphyton and detritus microbial communities in a subtropical wetland

The catabolic diversity of wetland microbial communities may be a sensitive indicator of nutrient loading or changes in environmental conditions. The objectives of this study were to assess the response of periphyton and microbial communities in water conservation area-2a (WCA-2a) of the Everglades to additions of C-substrates and inorganic nutrients. Carbon dioxide and CH₄ production rates were measured using 14 days incubation for periphyton, which typifies oligotrophic areas, and detritus, which is prevalent at P-impacted areas of WCA-2a. The wetland was characterized by decreasing P levels from peripheral to interior, oligotrophic areas. Microbial biomass and N mineralization rates were higher for oligotrophic periphyton than detritus. Methane production rates were also higher for unamended periphyton (80 mg CH₄-C kg⁻¹ d⁻¹) than detritus (22 mg CH₄-C kg⁻¹ d⁻¹), even though the organic matter content was higher for detritus (80%) than periphyton (69%). Carbon dioxide production for unamended periphyton (222 mg CO₂-C kg⁻¹ d⁻¹) was significantly greater than unamended detritus (84 mg CO₂-C kg⁻¹ d⁻¹). The response of the heterotrophic microbial community to added C-substrates was related to the nutrient status of the wetland, as substrate-induced respiration (SIR) was higher for detritus than periphyton. Amides and polysaccharides stimulated SIR more than other C-substrates, and methanogenesis was greater contributor to SIR for periphyton than detritus. Inorganic P addition stimulated CO₂ and CH₄ production for periphyton but not detritus, indicating a P limitation in the interior areas of WCA-2a. Continued nutrient loading into oligotrophic areas of WCA-2a or enhanced internal nutrient cycling may stimulate organic matter decomposition and further contribute to undesirable changes to the Everglades ecosystem caused by nutrient enrichment.     

Influence of suspended clay on phosphorus uptake by periphyton

We investigated the effect of suspended clay upon the phosphorus uptake rate exhibited by lotic periphyton communities. Suspended inorganic clays and periphyton are common to aquatic environments, and both can strongly influence physical and chemical water conditions. We used replicated artificial stream channels to test the prediction that suspended clay particles would affect the uptake of soluble reactive phosphorus (SRP) by periphyton. Commercially available kaolinite and bentonite clays were characterized for their aqueous suspension behavior and affinities for SRP. Periphyton was grown in a recirculating stream system and subjected to simultaneous suspended clay and SRP additions. SRP removal from solution, both in the presence and absence of suspended clays, was used to quantify SRP uptake parameters by periphyton. Clay type and concentrations of 20, 80, and 200 mg l⁻¹ had no significant effect upon SRP uptake rate exhibited by periphyton during three 90-min experiments. Less than 1% of SRP removal was attributable to the suspended clay load or artificial stream construction materials, based on clay isotherm data and material sorption studies, indicating that 99% of SRP removal was attributable to biotic uptake. Removal of SRP (as KH₂PO₄) was described by a first-order equation with rate constants ranging between 0.02 and 0.14 min⁻¹. Our results suggest that high turbidity conditions caused by suspended mineral clays have little immediate effect upon SRP removal from the water column by periphyton. Handling editor: D. Ryder     

磷模型在千岛湖水体污染预测中的应用研究

运用国际上通用的多个经验统计磷模型预测千岛湖目前的磷浓度水平,其中第6个模型最适合用于千岛湖的预测预报．利用该模型预测了磷负荷量分别减少1/4、1/2、3/4情况下,千岛湖水体中总磷浓度的响应．同时针对千岛湖营养水平控制的短、长期目标,利用模型计算出了所允许的总磷负荷量及入湖磷浓度．     

Quantifying the responses of calcareous periphyton crusts to rehydration: A microcosm study (Florida Everglades)

We examined the high-resolution temporal dynamics of recovery of dried periphyton crusts following rapid rehydration in a phosphorus (P)-limited short hydroperiod Everglades wetland. Crusts were incubated in a greenhouse in tubs containing water with no P or exogenous algae to mimic the onset of the wet season in the natural marsh when heavy downpours containing very low P flood the dry wetland. Algal and bacterial productivity were tracked for 20 days and related to compositional changes and P dynamics in the water. A portion of original crusts was also used to determine how much TP could be released if no biotic recovery occurred. Composition was volumetrically dominated by cyanobacteria (90%) containing morphotypes typical of xeric environments. Algal and bacterial production recovered immediately upon rehydration but there was a net TP loss from the crusts to the water in the first 2 days. By day 5, however, cyanobacteria and other bacteria had re-absorbed 90% of the released P. Then, water TP concentration reached a steady-state level of 6.6 μg TP/L despite water TP concentration through evaporation. Phosphomonoesterase (PMEase) activity was very high during the first day after rehydration due to the release of a large pre-existing pool of extracellular PMEase. Thereafter, the activity dropped by 90% and increased gradually from this low level. The fast recovery of desiccated crusts upon rehydration required no exogenous P or allogenous algae/bacteria additions and periphyton largely controlled P concentration in the water.     

Nitrogen and phosphorus removal rates using small algal turfs grown with dairy manure

Conservation and reuse of nitrogen (N) and phosphorus (P) from animalmanure is increasingly important as producers try to minimize transport ofthesenutrients from farms. An alternative to land spreading is to grow crops ofalgaeon the N and P present in the manure. The general goal of our research is toassess nutrient recovery from animal manure using attached algae. The specificobjective of this study was to evaluate the use of small subsections of algalturfs for determining N and P removal rates by attached algae under differentloading rates of dairy manure. Algae were grown in a laboratory–scalealgal turf scrubber (ATS) operated by recycling wastewater and adding manureeffluent daily. Replicate subsections (0.032 m²) ofalgal turf screens were removed and treated with five different loadings ofanaerobically digested dairy manure containing 5 to 80 mgL^–1 NH₄-N and 1 to 20 mgL^–1 PO₄-P over a 2-h incubationperiod. NH₄-N removal rates were biphasic with a fast initial ratefollowed by a slower rate. Biphasic rates were more pronounced for the lowestloading rates but less so for the higher ones. PO₄-P removal rateswere linear throughout the incubation period for all loading rates. N and Premoval rates increased with increasing loading rate and biomass. Inincubationsusing 1% dairy manure NH₄-N and PO₄-P removal ratesaveraged 0.72 and 0.33 g m^–2d^–1,respectively. These rates were approximately 5 to 8-fold lower than ratesmeasured on laboratory-scale ATS units using undisturbed turfs.     

Enzyme activity responses to nutrient loading in subtropical wetlands

Eutrophication caused by anthropogenic nutrient inputs is one of the greatest threats to the integrity of freshwater wetlands. The resultant changes in organic carbon cycling and nutrient mineralization may be expressed through increased decomposition rates, which are ultimately dependent on the metabolism of the resident microbial community. Specifically, microbial nutrient acquisition is controlled through the activity of enzymes, which are in turn influenced by local biogeochemical conditions. This study examines enzyme activities along distinct North-South P gradients within four distinct hydrologic units of the Florida Everglades. The results indicate that nutrient enriched sites exhibit lower N and P limitations on microbially constrained C mineralization, in addition to enhanced cellulose decomposition rates. Nutrient loading resulted in decreased microbial mobilization of resources for P mineralization, resulting in greater energetic allocation for C mineralization. Additionally, N appears to become less limiting to C mineralization in the enriched sites within Everglades National Park, the least P enriched area within the Everglades. A simple two component model, incorporating total P and the relationship between the enzymes involved in C and P mineralization accounted for between 46 and 92% of the variability in measured cellulose decomposition rates and thus demonstrates the significant influence that P loading plays in these systems. These results also suggest there is an environmental threshold TP concentration below which changes in enzyme-based resource allocation will not occur.     

Effects of benthic filamentous algae on the sediment–water interface in an acidic mining lake

Natural alkalinity generation by microbial sulphate reduction in acidic lakes is usually inhibited by the low pH and a low primary production which results in a lack of suitable organic carbon sources. In some acidic mining lakes mass developments of filamentous benthic algae occur. The effects of this periphyton layer on the biogeochemistry of the sediment–water interface were investigated by in situ microsensor measurements and laboratory incubations in Mining Lake Grünewalder Lauch (Germany). Microsensor measurements showed that the oxic–anoxic boundary was located in the periphyton layer and was moving up and down depending on light triggered photosynthesis. The sediment itself was permanently anoxic. The diurnal redox shift and the maintenance of neutral conditions in the periphyton layer lead to an effective precipitation of iron and phosphorus. Under the periphyton layer very high sulphate reduction rates up to 265 nmol cm⁻³ d⁻¹ were measured in the sediment. These are the highest rates reported for mining lakes so far. The microbial activity was high enough to keep the pH in the surface sediment neutral and contributed to natural alkalinity production. Handling editor: L. Naselli-Flores     

Ecological effects of low-level phosphorus additions on two plant communities in a neotropical freshwater wetland ecosystem

We conducted a low-level phosphorus (P) enrichment study in two oligotrophic freshwater wetland communities (wet prairies [WP] and sawgrass marsh [SAW]) of the neotropical Florida Everglades. The experiment included three P addition levels (0, 3.33, and 33.3 mg P m^–2 month^–1), added over 2 years, and used in situ mesocosms located in northeastern Everglades National Park, Fla., USA. The calcareous periphyton mat in both communities degraded quickly and was replaced by green algae. In the WP community, we observed significant increases in net aboveground primary production (NAPP) and belowground biomass. Aboveground live standing crop (ALSC) did not show a treatment effect, though, because stem turnover rates of Eleocharis spp., the dominant emergent macrophyte in this community, increased significantly. Eleocharis spp. leaf tissue P content decreased with P additions, causing higher C:P and N:P ratios in enriched versus unenriched plots. In the SAW community, NAPP, ALSC, and belowground biomass all increased significantly in response to P additions. Cladium jamaicense leaf turnover rates and tissue nutrient content did not show treatment effects. The two oligotrophic communities responded differentially to P enrichment. Periphyton which was more abundant in the WP community, appeared to act as a P buffer that delayed the response of other ecosystem components until after the periphyton mat had disappeared. Periphyton played a smaller role in controlling ecosystem dynamics and community structure in the SAW community. Our data suggested a reduced reliance on internal stores of P by emergent macrophytes in the WP that were exposed to P enrichment. Eleocharis spp. rapidly recycled P through more rapid aboveground turnover. In contrast, C. jamaicense stored added P by initially investing in belowground biomass, then shifting growth allocation to aboveground tissue without increasing leaf turnover rates. Our results suggest that calcareous wetland systems throughout the Caribbean, and oligotrophic ecosystems in general, respond rapidly to low-level additions of their limiting nutrient.     

Short-term changes in phosphorus storage in an oligotrophic Everglades wetland ecosystem receiving experimental nutrient enrichment

Natural, unenriched Evergladeswetlands are known to be limited by phosphorus(P) and responsive to P enrichment. However,whole-ecosystem evaluations of experimental Padditions are rare in Everglades or otherwetlands. We tested the response of theEverglades wetland ecosystem to continuous,low-level additions of P (0, 5, 15, and30 g L^–1 above ambient) in replicate,100 m flow-through flumes located in unenrichedEverglades National Park. After the first sixmonths of dosing, the concentration andstanding stock of phosphorus increased in thesurface water, periphyton, and flocculentdetrital layer, but not in the soil or macrophytes. Of the ecosystem components measured, total P concentration increased the most in the floating periphyton mat (30 g L^–1: mean = 1916 g P g^–1, control: mean =149 g P g^–1), while the flocculentdetrital layer stored most of the accumulated P(30 g L^–1: mean = 1.732 g P m^–2,control: mean = 0.769 g P m^–2). Significant short-term responsesof P concentration and standing stock wereobserved primarily in the high dose (30 gL^–1 above ambient) treatment. Inaddition, the biomass and estimated P standingstock of aquatic consumers increased in the 30and 5 g L^–1 treatments. Alterationsin P concentration and standing stock occurredonly at the upstream ends of the flumes nearestto the point source of added nutrient. Thetotal amount of P stored by the ecosystemwithin the flume increased with P dosing,although the ecosystem in the flumes retainedonly a small proportion of the P added over thefirst six months. These results indicate thatoligotrophic Everglades wetlands respondrapidly to short-term, low-level P enrichment,and the initial response is most noticeable inthe periphyton and flocculent detrital layer.     

Phosphorus cycling and partitioning in an oligotrophic Everglades wetland ecosystem: a radioisotope tracing study

1. Our goal was to quantify short‐term phosphorus (P) partitioning and identify the ecosystem components important to P cycling in wetland ecosystems. To do this, we added P radiotracer to oligotrophic, P‐limited Everglades marshes. ³²PO₄ was added to the water column in six 1‐m² enclosed mesocosms located in long‐hydroperiod marshes of Shark River Slough, Everglades National Park. Ecosystem components were then repeatedly sampled over 18 days. 2. Water column particulates (>0.45 μm) incorporated radiotracer within the first minute after dosing and stored 95–99% of total water column ³²P activity throughout the study. Soluble (<0.45 μm) ³²P in the water column, in contrast, was always <5% of the ³²P in surface water. Periphyton, both floating and attached to emergent macrophytes, had the highest specific activity of ³²P (Bq g^?131P) among the different ecosystem components. Fish and aquatic macroinvertebrates also had high affinity for P, whereas emergent macrophytes, soil and flocculent detrital organic matter (floc) had the lowest specific activities of radiotracer. 3. Within the calcareous, floating periphyton mats, 81% of the initial ³²P uptake was associated with Ca, but most of this ³²P entered and remained within the organic pool (Ca‐associated = 14% of total) after 1 day. In the floc layer, ³²P rapidly entered the microbial pool and the labile fraction was negligible for most of the study. 4. Budgeting of the radiotracer indicated that ³²P moved from particulates in the water column to periphyton and floc and then to the floc and soil over the course of the 18 day incubations. Floc (35% of total) and soil (27%) dominated ³²P storage after 18 days, with floating periphyton (12%) and surface water (10%) holding smaller proportions of total ecosystem ³²P. 5. To summarise, oligotrophic Everglades marshes exhibited rapid uptake and retention of labile ³²P. Components dominated by microbes appear to control short‐term P cycling in this oligotrophic ecosystem.     

Effects of hydrologic and water quality drivers on periphyton dynamics in the southern Everglades

Everglades periphyton mats are tightly-coupled autotrophic (algae and cyanobacteria) and heterotrophic (eubacteria, fungi and microinvertebrates) microbial assemblages. We investigated the effect of water column total phosphorus and nitrogen concentrations, water depth and hydroperiod on periphyton of net production, respiration, nutrient content, and biomass. Our study sites were located along four transects that extended southward with freshwater sheetflow through sawgrass-dominated marsh. The water source for two of the transects were canal-driven and anchored at canal inputs. The two other transects were rain-driven (ombrotrophic) and began in sawgrass-dominated marsh. Periphyton dynamics were examined for upstream and downstream effects within and across the four transects. Although all study sites were characterized as short hydroperiod and phosphorus-limited oligotrophic, they represent gradients of hydrologic regime, water source and water quality of the southern Everglades. Average periphyton net production of 1.08 mg C AFDW⁻¹ h⁻¹ and periphyton whole system respiration of 0.38 mg C AFDW⁻¹ h⁻¹ rates were net autotrophic. Biomass was generally highest at ombrotrophic sites and sites downstream of canal inputs. Mean biomass over all our study sites was high, 1517.30 g AFDW m⁻². Periphyton was phosphorus-limited. Average periphyton total phosphorus content was 137.15 μg P g⁻¹ and average periphyton total N:P ratio was 192:1. Periphyton N:P was a sensitive indicator of water source. Even at extremely low mean water total phosphorus concentrations ( ≤ 0.21 μmol l⁻¹), we found canal source effects on periphyton dynamics at sites adjacent to canal inputs, but not downstream of inflows. These canal source effects were most pronounced at the onset of wet season with initial rewetting. Spatial and temporal variability in periphyton dynamics could not solely be ascribed to water quality, but was often associated with both hydrology and water source.