Responses of sawgrass and spikerush to variation in hydrologic drivers and salinity in Southern Everglades marshes

Aboveground net primary production (ANPP) by the dominant macrophyte and plant community composition are related to the changing hydrologic environment and to salinity in the southern Everglades, FL, USA. We present a new non-destructive ANPP technique that is applicable to any continuously growing herbaceous system. Data from 16 sites, collected from 1998 to 2004, were used to investigate how hydrology and salinity controlled sawgrass (Cladium jamaicense Crantz.) ANPP. Sawgrass live biomass showed little seasonal variation and annual means ranged from 89 to 639 gdw m⁻². Mortality rates were 20–35% of live biomass per 2 month sampling interval, for biomass turnover rates of 1.3–2.5 per year. Production by C. jamaicense was manifest primarily as biomass turnover, not as biomass accumulation. Rates typically ranged from 300 to 750 gdw m⁻² year⁻¹, but exceeded 1000 gdw m⁻² year⁻¹ at one site and were as high as 750 gdw m⁻² year⁻¹ at estuarine ecotone sites. Production was negatively related to mean annual water depth, hydroperiod, and to a variable combining the two (depth-days). As water depths and hydroperiods increased in our southern Everglades study area, sawgrass ANPP declined. Because a primary restoration goal is to increase water depths and hydroperiods for some regions of the Everglades, we investigated how the plant community responded to this decline in sawgrass ANPP. Spikerush (Eleocharis sp.) was the next most prominent component of this community at our sites, and 39% of the variability in sawgrass ANPP was explained by a negative relationship with mean annual water depth, hydroperiod, and Eleocharis sp. density the following year. Sawgrass ANPP at estuarine ecotone sites responded negatively to salinity, and rates of production were slow to recover after high salinity years. Our results suggest that ecologists, managers, and the public should not necessarily interpret a decline in sawgrass that may result from hydrologic restoration as a negative phenomenon.     

Cellulolytic, fermentative, and methanogenic guilds in benthic periphyton mats from the Florida Everglades

Phosphorus enrichment caused by runoff from agricultural areas has resulted in ecosystem-level changes in the northern Florida Everglades, including a loss of periphyton mats from nutrient-impacted areas. The potential for methanogenesis resulting from the anaerobic decomposition of cellulose and fermentation products, and the microorganisms responsible for these processes, were studied in mats from a region not impacted by nutrient enrichment. Methane was produced from periphyton incubated with cellulose, propionate, butyrate, and formate, with an accumulation of fatty acids in incubations. The accumulation of fatty acids may have been caused by the inhibition of syntrophic oxidation, a potentially significant route for methane production in soils. Sequence analysis of 16S rRNA genes characteristic of Clostridium, the primary genus responsible for anaerobic decomposition and fermentation in soils of the area, indicated that Clostridium Cluster I assemblages present in the mat differed from those in the soils of the area. Significantly, sequences characteristic of the Clostridium group that dominates the soils of the area, group XIV, were not detected in the mat. These results indicate that benthic periphyton is probably a significant source of methane in the Everglades, and the responsible microorganisms differ significantly from those in the soils of the area.     

Comparative study of periphyton community structure in long and short-hydroperiod Everglades marshes

The Florida Everglades is a mosaic of short and long-hydroperiod marshes that differ in the depth, duration, and timing of inundation. Algae are important primary producers in widespread Everglades’ periphyton mats, but relationships of algal production and community structure to hydrologic variability are poorly understood. We quantified differences in algal biomass and community structure between periphyton mats in 5 short and 6 long-hydroperiod marshes in Everglades National Park (ENP) in October 2000. We related differences to water depth and total phosphorus (TP) concentration in the water, periphyton and soils. Long and short-hydroperiod marshes differed in water depth (73 cm vs. 13 cm), periphyton TP concentrations (172μg g⁻¹ vs. 107 μg g⁻¹, respectively) and soil TP (284 μg g⁻¹ vs. 145 μg g⁻¹). Periphyton was abundant in both marshes, with short-hydroperiod sites having greater biomass than long-hydroperiod sites (2936 vs. 575 grams ash-free dry mass m⁻²). A total of 156 algal taxa were identified and separated into diatom (68 species from 21 genera) and “soft algae” (88 non-diatom species from 47 genera) categories for further analyses. Although diatom total abundance was greater in long-hydroperiod mats, diatom species richness was significantly greater in short- hydroperiod periphyton mats (62 vs. 47 diatom taxa). Soft algal species richness was greater in long-hydroperiod sites (81 vs. 67 soft algae taxa). Relative abundances of individual taxa were significantly different among the two site types, with soft algal distributions being driven by water depth, and diatom distributions by water depth and TP concentration in the water and periphyton. Periphyton communities differ between short and long-hydroperiod marshes, but because they share many taxa, alterations in hydroperiod could rapidly promote the alternate community. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Effects of shading on calcareous benthic periphyton in a short-hydroperiod oligotrophic wetland (Everglades, FL, USA)

The effects of shade on benthic calcareous periphyton were tested in a short-hydroperiod oligotrophic subtropical wetland (freshwater Everglades). The experiment was a split-plot design set in three sites with similar environmental characteristics. At each site, eight randomly selected 1-m² areas were isolated individually in a shade house, which did not spectrally change the incident irradiance but reduced it quantitatively by 0, 30, 50, 60, 70, 80, 90 and 98%. Periphyton mat was sampled monthly under each shade house for a 5 month period while the wetland was flooded. Periphyton was analyzed for thickness, DW, AFDW, chlorophyll a (chl a) and incubated in light and dark BOD bottles at five different irradiances to assess its photosynthesis–irradiance (PI) curve and respiration. The PI curves parameters P _max, I _k and eventually the photoinhibition slope (β) were determined following non-linear regression analyses. Taxonomic composition and total algal biovolume were determined at the end of the experiment. The periphyton composition did not change with shade but the PI curves were significantly affected by it. I _k increased linearly with increasing percent irradiance transmittance (%IT = 1−%shade). P _max could be fitted with a PI curve equation as it increased with %IT and leveled off after 10%IT. For each shade level, the PI curve was used to integrate daily photosynthesis for a day of average irradiance. The daily photosynthesis followed a PI curve equation with the same characteristics as P _max vs. %IT. Thus, periphyton exhibited a high irradiance plasticity under 0–80% shade but could not keep up the same photosynthetic level at higher shade, causing a decrease in daily GPP at 98% shade levels. The plasticity was linked to an increase in the chl a content per cell in the 60–80% shade, while this increase was not observed at lower shade likely because it was too demanding energetically. Thus, chl a is not a good metric for periphyton biomass assessment across variously shaded habitats. It is also hypothesized that irradiance plasticity is linked to photosynthetic coupling between differently comprised algal layers arranged vertically within periphyton mats that have different PI curves.     

Spatial and seasonal patterns of periphyton biomass and productivity in the northern Everglades,Florida, U.S.A.

We sampled periphyton in dominant habitats at oligotrophic and eutrophic sites in the northern Everglades during the wet and the dryseasons to determine the effects of nutrient enrichment on periphytonbiomass, taxonomic composition, productivity, and phosphorus storage. Arealbiomass was high (100–1600 g ash-free dry mass [AFDM]m⁻²) in oligotrophic sloughs and in stands of the emergentmacrophyte Eleocharis cellulosa, but was low in adjacent stands of sawgrass,Cladium jamaicense (7–52 g AFDM m⁻²). Epipelon biomasswas high throughout the year at oligotrophic sites whereas epiphyton andmetaphyton biomass varied seasonally and peaked during the wet season.Periphyton biomass was low (3–68 g AFDM m⁻²) and limitedto epiphyton and metaphyton in open-water habitats at eutrophic sites andwas undetectable in cattail stands (Typha domingensis) that covered morethan 90% of the marsh in these areas. Oligotrophic periphytonassemblages exhibited strong seasonal shifts in species composition and weredominated by cyanobacteria (e.g., Chroococcus turgidus, Scytonema hofmannii)during the wet season and diatoms (e.g. Amphora lineolata, Mastogloiasmithii) during the dry season. Eutrophic assemblages were dominated byCyanobacteria (e.g., Oscillatoria princeps) and green algae (e.g., Spirogyraspp.) and exhibited comparatively little seasonality. Biomass-specific grossprimary productivity (GPP) of periphyton assemblages in eutrophic openwaters was higher than for comparable slough assemblages, but areal GPP wassimilar in these eutrophic (0.9–9.1 g C m⁻²d⁻¹) and oligotrophic (1.75–11.49 g C m⁻²d⁻¹) habitats. On a habitat-weighted basis, areal periphytonGPP was 6- to 30-fold lower in eutrophic areas of the marsh due to extensiveTypha stands that were devoid of periphyton. Periphyton at eutrophic siteshad higher P content and uptake rates than the oligotrophic assemblage, butstored only 5% as much P because of the lower areal biomass.Eutrophication in the Everglades has resulted in a decrease in periphytonbiomass and its contribution to marsh primary productivity. These changesmay have important implications for efforts to manage this wetland in asustainable manner. This revised version was published online in July 2006 with corrections to the Cover Date.     

Trophic transfer of methyl mercury in the northern Florida Everglades

There are spatial differences in methyl mercury (MeHg) concentrations in biota in Water Conservation Areas 2 and 3 in the Everglades, with higher concentrations generally found in the southern areas. Fish and hemipterans had the most MeHg on a wet weight basis, with levels exceeding 30 ng g^-1. The magnitude of MeHg accumulation in biota varies seasonally and does not always appear to be associated with changes in water column concentration. This is exemplified by periphyton, the base of the foodweb in the Everglades, at a high nutrient sampling site. Although limited in scope, MeHg concentrations presented for biota provide insight into beginning to understand the dynamic nature of Hg transfer in the Everglades foodweb on a spatial and temporal basis.     

Effects of riparian leaf dynamics on periphyton photosynthesis and light utilisation efficiency

1. Streambed light regimes change dramatically when riparian trees gain leaves in spring and lose them in autumn. This study examined the effect of these changes on periphyton photosynthetic characteristics, primary production, and light utilisation efficiency in two eastern Tennessee streams. 2. Photosynthesis–irradiance responses were measured at intervals covering leaf emergence and abscission in spring and autumn. Photosynthetic efficiency (α^chl) increased with declining streambed irradiances during spring leaf emergence, but returned to pre‐emergence values after autumn leaf fall. The onset of photosaturation (I_k) displayed the opposite pattern, decreasing during leaf emergence and increasing after leaf fall. Both α^chl and I_k were closely associated (P < 0.01) with daily integrated streambed irradiance, as were periphyton carotenoids. Internal shading by photoprotective carotenoids is hypothesised to account for lower α^chl when streambed irradiances are high. 3. An in situ shading experiment confirmed that the temporal changes observed in periphyton photosynthetic characteristics and carotenoids were primarily the result of changing light levels and not other environmental factors (e.g. nutrients, temperature). 4. Daily chlorophyll‐specific primary production (PP^chl) was calculated with P–I models and recorded streambed irradiances. In both streams, PP^chl was the highest in early spring when trees were leafless, and then declined markedly as leaves emerged, reaching a minimum in summer. PP^chl increased after leaf abscission, but was still lower than it was in early spring, when the sun was higher and daylength was longer. A hyperbolic tangent equation fit to PP^chl and daily integrated irradiance (r²=0. 85) suggested that primary production was light saturated at 4–8 mol m^–2 d^–1. 5. Light utilisation efficiency (Ψ) increased 10‐fold during leaf emergence. Photosaturation at high irradiances and photoacclimation at lower irradiances were responsible for a negative hyperbolic relationship between Ψ and daily integrated irradiance.     

Elevated light and nutrients alter the nutritional quality of stream periphyton

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Influence of water depth on nest success of the endangered Cape Sable seaside sparrow in the Florida Everglades

The restoration of the Florida Everglades rests largely on the ability of managers to re-create a more natural hydrologic regime throughout the remaining natural areas. The Cape Sable seaside sparrow, an endangered subspecies endemic to the freshwater marl prairies of the Everglades, has suffered from changes in the depth and the timing of water flows through its habitat. However, it remains unclear what temporal and spatial aspects of water inputs (both managed and natural) affect nesting success. We monitored 429 nests in two of the six extant sparrow subpopulations over 10 breeding seasons and a variety of water levels. Using an information-theoretic approach, we find that nests initiated early in the breeding season experience substantially higher success rates than those initiated later. We suggest that this seasonal effect is due to a change in predator abundance or activity levels as the season progresses, which are tied to the increase in water levels that accompany the onset of the wet season. In addition, nest success is influenced to a lesser degree by where sparrows choose to nest across the landscape, the height of base water levels within the sparrow's breeding season and the height of water levels when nests are active. Our observation of extreme variability in nest success over the span of a single season suggests that successful late-season breeding, although shown to be important for population recovery, is a rare event. Management actions that maximize the success of late-season broods or increase the number of early broods are warranted, but the ecosystem implications of such actions are poorly understood.     

白洋淀附着藻类的初级生产力及其与水质的关系

附着藻类是湖泊中主要的生产者,尤其是草型湖泊。但与浮游藻类相比,针对附着藻类初级生产的研究还相对较少。采用原位调查与实验模拟相结合的方法测定2014—2015年间白洋淀附植藻类和附泥藻类的现存量和初级生产力,并对附着藻类初级生产与白洋淀水体理化参数的关系进行分析。结果表明,不同采样季节的附植藻类和附泥藻类的叶绿素a分别为34.83—245.22μg/cm~2和26.08—297.40μg/cm~2,无灰干重分别为0.46—5.21g/m~2和0.61—5.81g/m~2。两种附着藻类的生物量都在8月最高,4月和11月最低。空间分布上,南刘庄、府河入口的附着藻类生物量显著高于采蒲台和枣林庄。白洋淀附植藻类和附泥藻类的年均总初级生产分别为494.20mg C m~(-2)d~(-1)和474.45mg C m~(-2)d~(-1),呼吸速率为522.63mg C m~(-2)d~(-1)和508.98mg C m~(-2)d~(-1),净初级生产为-28.44mg C m~(-2)d~(-1)和-34.52mg C m~(-2)d~(-1)。白洋淀附着藻类初级生产力具有明显的时空分布规律,8月最高,6月次之,4月和11月最低,空间分布呈自西向东递减的趋势,在府河入淀口和南刘庄处最高,枣林庄和采蒲台最低。水质较好的区域的净初级生产力为正值,表明这些区域附着藻类以自养型群落为主,水质较差区域的净初级生产力为负值,则该区域以异养型群落为主。运用冗余分析法(RDA)探讨附着藻类与水质因子之间的关系,并采用向前引入法对水质因子进行逐步筛选,Monte Carlo置换检验结果显示,总磷、浮游植物叶绿素a、高锰酸盐指数、氨氮、水温、透明度、溶解氧和氮磷比是影响附着藻类生物量和初级生产的关键水质因子。附着藻类的总初级生产与水体富营养化程度呈正相关关系。     

UV-B irradiance gradient affects photosynthesis and pigments but not food quality of periphyton

• 1 This laboratory study examined the effect of a gradient of UV‐B radiation (280–320 nm) on photosynthesis and food quality of periphyton, the trophic base of many freshwater benthic communities. Four irradiances of UV‐B (0, 0.6, 1.2, and 2.3 W m^‐2) were delivered by UV‐B lamps (313 nm peak irradiance) over a 13‐day period in the first experiment and over a 4‐h period in the second experiment. These irradiances were roughly equivalent to 0, 1, 2, and 4 times the ambient biologically effective (DNA) midsummer, midday UV‐B irradiance in Tennessee.
• 2 Rates of photosynthesis and photosynthetic pigments were significantly reduced by irradiances greater than ambient during the 13‐day experiment, suggesting that food supply rates to grazers would be depressed by increases in current UV‐B levels. Effects on community structure were minor, but mean diatom cell size decreased at higher UV‐B irradiances.
• 3 Irradiated periphyton was fed in surplus to juvenile snails (Physella gyrina) in the first experiment as a bioassay for food quality. Snail growth was the same on all four diets, suggesting that UV‐B did not affect food quality. Nitrogen and phosphorus content of the periphyton were not affected by UV‐B, either.
• 4 Photosynthesis by low‐biomass periphyton in the second experiment was significantly depressed by irradiances above ambient after only 4 h. Photosynthesis by the high biomass periphyton was not significantly affected by UV‐B, suggesting that self‐shading reduced UV‐B effects.

     

不同氮磷浓度下周丛生物对水体中磺胺和恩诺沙星的去除

周丛生物膜是一种对水体污染物净化的新兴生物技术。有关水体不同氮磷营养水平下周丛生物对水体抗生素类污染物去除作用的研究还未见报道。本研究设置4个氮磷营养盐浓度水平[N-P (mg·L^-1):2-0.2、5-0.5、8-0.8、11-1.1],用塑料筐装置在室外培养周丛生物膜,对其生长、光合活力、物种组成以及对磺胺和恩诺沙星去除作用进行中型模拟试验。结果表明: 各处理组中周丛生物的生物量随培养时间的增加而升高,光合色素含量和光合活力则呈现先降低后上升的“单峰”模式,表明生物膜中的藻类会受到抗生素的胁迫,但可快速适应并恢复活力。除此之外,不同氮磷浓度处理造成各组生物群落组成差异,随营养盐浓度的升高,周丛藻类物种丰富度逐渐下降,但各处理胶网藻和小球藻都具有较高的相对丰度;16S rRNA高通量测序发现,根瘤菌科、放线菌门和莫拉氏菌科菌群在(N-P)2-0.2组显著富集,而几丁质嗜菌科在4个处理中的相对丰度都处在最高水平。所有处理的磺胺去除率均高于50%,而恩诺沙星去除率均达到90%以上,其中,(N-P)2-0.2 mg·L^-1组对磺胺的去除率(65.8%)显著高于其他各组,但各处理对恩诺沙星的去除率差异不显著,表明周丛生物在较宽的N-P营养水平范围内对磺胺和恩诺沙星均具有良好的去除能力。各处理组对水体可溶性氮的去除效果不明显,但对可溶性磷的去除效果显著。本研究为水体磺胺和恩诺沙星的生态去除提供了基础数据,为研发水体抗生素类新型污染物生态去除技术提供了新思路。     

Historical changes in the conductivity and ionic charateristics of the source water for the Shark River Slough,Everglades National Park,Florida, U.S.A.

Man-made changes in the hydrological regime of South Florida have significantly altered the conductivity and ionic composition of water in the Shark River Slough system of Everglades National Park. The shift in water inputs from unregulated marsh water flow to regulated delivery of canal water has resulted in a 140% increase in conductivity and 149% increase in total ionic concentration since the early 1960s. Associated with this change has been a 300–400% increase in sodium and chloride concentrations in the waters entering the Shark River Slough of Everglades National Park.     

Rapid responses of vegetation to hydrological changes in Taylor Slough, Everglades National Park, Florida, USA

We analyzed the dynamics of freshwater marsh vegetation of Taylor Slough in eastern Everglades National Park for the 1979 to 2003 period, focusing on cover of individual plant species and on cover and composition of marsh communities in areas potentially influenced by a canal pump station (“S332”) and its successor station (“S332D”). Vegetation change analysis incorporated the hydrologic record at these sites for three intervals: pre-S332 (1961–1980), S332 (1980–1999), post-S332 (1999–2002). During S332 and post-S332 intervals, water level in Taylor Slough was affected by operations of S332 and S332D. To relate vegetation change to plot-level hydrological conditions in Taylor Slough, we developed a weighted averaging regression and calibration model (WA) using data from the marl prairies of Everglades National Park and Big Cypress National Preserve. We examined vegetation pattern along five transects. Transects 1–3 were established in 1979 south of the water delivery structures, and were influenced by their operations. Transects 4 and 5 were established in 1997, the latter west of these structures and possibly under their influence. Transect 4 was established in the northern drainage basin of Taylor Slough, beyond the likely zones of influence of S332 and S332D. The composition of all three southern transects changed similarly after 1979. Where muhly grass (Muhlenbergia capillaris var. filipes) was once dominant, sawgrass (Cladium jamaicense), replaced it, while where sawgrass initially predominated, hydric species such as spikerush (Eleocharis cellulosa Torr.) overtook it. Most of the changes in species dominance in Transects 1–3 occurred after 1992, were mostly in place by 1995–1996, and continued through 1999, indicating how rapidly vegetation in seasonal Everglades marshes can respond to hydrological modifications. During the post-S332 period, these long-term trends began reversing. In the two northern transects, total cover and dominance of both muhly grass and sawgrass increased from 1997 to 2003. Thus, during the 1990’s, vegetation composition south of S332 became more like that of long hydroperiod marshes, but afterward it partially returned to its 1979 condition, i.e., a community characteristic of less prolonged flooding. In contrast, the vegetation change along the two northern transects since 1997 showed little relationship to hydrologic status.     

Nutrient and hydrologic budgets of a great lakes coastal freshwater wetland during a drought year

A coastal wetland along Lake Erie (Ohio, U.S.A.) was studied to determine hydrologic and phosphorus budgets and spatial and temporal variation of phosphorus and related chemical parameters. The wetland was influenced by changing Lake Erie water levels, seiches, shifting shoreline sediments, and watershed inflow during a year of severe drought. The water budget for a 7-month period (March – September, 1988) had average inflow of 15 200 m³ day^–1 from the watershed and 3.5 m³ day^–1 from Lake Erie. The wetland increased in volume by 700 m³ day^–1 despite a drought that resulted in 80% more evapotranspiration than rainfall as a barrier beach isolated the wetland from Lake Erie for 77% of the study period. Conductivity decreased by 34% as water flowed through the wetland and turbidity and total suspended solids were variable and statistically similar at inflow and outflow. Average total phosphorus concentrations in the inflow and outflow were also similar (247 and 248 µg P l^–1 respectively) although total soluble phosphorus and soluble reactive phosphorus decreased significantly (=0.05) from inflow to outflow (averages 94 to 45 µg P l^–1 and 7.5 to 4.0 µg P l^–1 respectively). Nutrient budgets from field data estimate a retention of 36% of the phosphorus, presumably in the sediments (0.8 mg P m^–2 day^–1). A general nutrient retention model, an estimated deposition rate from a sediment core and a simulation model predicted higher mass retention of phosphorus but similar percentage retention.SommaireUn marecage qui côtoie le lac Erie (USA) a servi de site expérimental pour en déterminer les budgets d'eau et de phosphore, de même que pour la variation spatiale et temporelle du phosphore et d'autres facteurs chimiques. Le marécage a été influencé par: niveaux d'eau qui changeaient; seiches; sédiments mouvants du littoral; et afflux de la ligne de partage des eaux dans une année de grande sécheresse. Le budget d'eau dans une période de 7 mois (mars–septembre 1988) montre un afflux de 15 200 m³ jour^–1 de la ligne de partage, et 3.5 m³ jour^–1 du lac Erie. Le volume du marécage a augmenté par 700 m³ jour^–1 malgré une sécheresse qui a produit plus d'évapotranspiration (80%) que de pluie pendant qu'une plage-obstacle a isolé le marecage du lac Erie pendant 77% de la période d'observation. La conductivité a diminué par 34% pendant que l'eau coulait, et la turbidité et les TSS ont varié, tout en démontrant des statistiques similaires à l'afflux et au déversement. Les moyennes pour les concentrations du total du phosphore à l'afflux et au déversement ont été similaires (247 and 248 µg P l^–1), quoique le TSP et le SRP ont diminué (=0.05) de l'afflux au déversement (donant des moyennes de 94 à 45 µg P l^–1 et de 7.5 à 4.0 µg P l'^–1). Les budgets de substances nutritives pour les données suggèrent une reténtion de 36% du phosphore, évidemment dans les sédiments (0.8 mg P m^–2 jour^–1). Un modèle pour la rétention des nutrients, un taux de déposition, estimé par un noyau de sédiments, et une simulation avaient prédit un plus grand taux de rétention de phosphore, mais un pourcentage similaire pour la rétention.From a paper presented at the Third International Wetlands Conference, 19–23 September, 1988, University of Rennes, France.     

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.     

Low algal carbon content and its effect on the C : P stoichiometry of periphyton

1. We examined the contribution of algal cells to periphytic organic carbon and assessed the effects of variable biomass composition on the carbon : phosphorus (C : P) ratio of periphyton. We compiled more than 5000 published and unpublished observations of periphytic carbon : chlorophyll a (C : Chl) ratios, an index of algal prevalence, from a variety of substrata collected from lake and low‐salinity coastal habitats. In addition, we converted estimates of algal biovolume into algal C to obtain an independent measure of cellular algal carbon in periphyton. This information was used in a model relating periphyton C : P ratio to algal cellular carbon, the algal C : P ratio, and the C : P ratio of non‐algal organic matter in periphyton. 2. The mean C : Chl ratio of periphyton (405) was relatively high with values in >25% of the samples exceeding 500. On average, 8.4% of total periphyton C was accounted for by C in algal cells. Only 15% of samples were found to have more than 15% periphyton C in cellular algal carbon. Our model showed a nonlinear relationship between periphytic C : P ratios and the C : P ratio of algal cells in the periphyton when non‐algal organic matter was present. However, even at relatively low cellular algal C (<10% of total C), algal C : P ratios can strongly affect the C : P ratio of periphyton as a whole (i.e. algal cells plus other organic matter). 3. The high C : Chl ratios and the low biovolume‐derived algal C of periphyton samples in our data set indicate that algal cells are typically a minor component of organic carbon in periphyton, However, this minor contribution would not preclude algal cellular stoichiometry from notably influencing periphyton C : P ratios.     

Controls on periphyton biomass in heterotrophic streams

1. Headwater streams of the Hubbard Brook Experimental Forest (HBEF) are typically characterised by a periphyton assemblage of low biomass and diversity. However, periphyton blooms have been observed following catchment deforestation experiments and occasionally during the annual spring thaw before canopy leaf‐out. 2. There is pronounced seasonal variation in both nutrient and light availability in HBEF streams. Stream water nitrogen (N) concentrations and light levels are higher before canopy leaf‐out and after leaf senescence and are lower during the growing season. Periphyton accrual rates also change seasonally; they are highest in spring prior to leaf‐out and significantly lower during summer and in autumn. 3. Periphyton biomass rarely responded positively to in‐situ experimental enrichment with nitrogen or phosphorus. In the summer, nutrient enrichment overall had no effect on periphyton biomass, while outside the growing season N enrichment had inhibitory effects on periphyton. 4. Despite these experimental results, surveys of ambient chlorophyll a concentrations in streams across the HBEF demonstrated no relationship between streamwater dissolved inorganic N or P concentrations and benthic chlorophyll a. 5. Our results suggest that HBEF periphyton communities are not closely regulated by nutrient availability, even during periods of high light availability. The inhibitory effects of nutrient enrichment outside the growing season are interesting, but further research is necessary to elucidate the mechanisms driving these responses.     

Interactions between nutrient availability and hydroperiod shape macroinvertebrate communities in Florida Everglades marshes

Hydroperiod and nutrient status are known to influence aquatic communities in wetlands, but their joint effects are not well explored. I sampled floating periphyton mat and flocculent detritus (floc) infaunal communities using 6-cm diameter cores at short- and long-hydroperiod and constantly inundated sites across a range of phosphorus (P) availability (total phosphorus in soil, floc and periphyton). Differences in community structure between periphyton and floc microhabitats were greater than any variation attributable to hydroperiod, P availability, or other spatial factors. Multivariate analyses indicated community structure of benthic-floc infauna was driven by hydroperiod, although crowding (no. g⁻¹ AFDM) of individual taxa showed no consistent responses to hydroperiod or P availability. In contrast, community structure of periphyton mat infauna was driven by P availability, while densities of mat infauna (no. m⁻²) were most influenced by hydroperiod (+correlations). Crowding of mat infauna increased significantly with P availability in short-hydroperiod marshes, but was constant across the P gradient in long-hydroperiod marshes. Increased abundance of floating-periphyton mat infauna with P availability at short-hydroperiod sites may result from a release from predation by small fish. Community structure and density were not different between long-hydroperiod and constantly inundated sites. These results have implications for the use of macroinvertebrates as indicators of water quality in wetlands and suggest the substrate sampled can influence interpretation of ecological responses observed in these communities.     

Effects of the water discharge on periphyton abundance and diversity in a large river (River Danube,Hungary)

This paper examines the relevance of intermediate disturbance theory in the context of in a large river the algal flora attaching to artificial substrata. It was observed that the theory is in good agreement with most of the communities analysed, however, with different frequency intervals compared to phytoplankton. Floods provided the most significant disturbances. As a rough generalization, we can say that in case of floods following each other in 8–14 days, respectively, the disturbance is of medium frequency. In case of 8 days, high frequency is more typical while in case of 14 days, low frequency is more characteristic. Owing to the fact that riverine periphytic algal organisms are attached in different ways and with differing efficiencies, the changes in the total mass occurring as a result of changes in water discharge lead to changes in diversity. The analysis of individual numbers can help in investigating the intensity of the disturbing effect on the algal communities. Negative correlation was found between water discharge and numbers of individuals, that is, the numbers of algae increase with low water discharge and decrease with high water level in the river. This second observation is valid only within a certain range of discharges (in this case up to 100 m³ s^–1), which will be specific to particular rivers and individual reaches. Below the upper limit of the range, the increased water flows carry more nutrients to the organisms but with no severe wash-off effect. Beyond the upper limit (in this case in range 100–400 m³ s^–1) the numbers of individuals is roughly in inverse proportion to the wash-off effect of the current, and the community is in equilibrium. In cases when discharge surpasses 400 m³ s^–1 decrease in individual numbers is general. We suggest that in the environments similar to the study area, the periphyton of the artificial substrata (e.g., pontoons) undergo similar processes. In respect of the periphyton formed on the surface of the riverbeds in large rivers with considerable changes in water level, a more complex system can be supposed where part of the periphyton is periodically dried and flooded alternately.