John D. Wehr

USE OF PHYTOPLANKTON IN LARGE RIVER MANAGEMENT

Historically, rivers have served as sources of drinking water, fisheries resources, transportation routes, irrigation supplies, and waste removal systems. Human civilization has had many major effects on rivers, dating back more than 5000 years when Egyptians built dams on the Nile to supply water for crops and human consumption. Today, management of large rivers requires a balance between human needs and ecological integrity, although until quite recently, ecological principles have played a minor role in river management (Edwards 1995). Planktonic algae are an important part of these issues because they play a central role in the functioning of large rivers. Algal communities are major producers of organic carbon in larger rivers, are a food source for planktonic consumers, and may represent the primary oxygen source in many low-gradient rivers (Thorp and Delong 1994, Kohler 1995, Reynolds and Descy 1996). Phytoplankton are responsive to excessive supplies of inorganic nutrients and may pose problems in long stretches of rivers with cultural eutrophication, but may also enhance water quality for humans in rivers affected by agricultural or industrial uses. Algal communities of river systems consist not only of suspended algae, but also a diverse benthic assemblage of macrophytic forms, smaller epilithic species, epiphytes, and sediment-dwelling forms (Reynolds 1996). This review focuses on the use of planktonic algae in river management because of their central importance in larger rivers and because of the growing need for ecosystem-level studies on river plankton.

Trophic relations in a stream food web: importance of fatty acids for macroinvertebrate consumers

Abstract  Our study is a first attempt to characterize seasonal fatty acid (FA) profiles of foodweb components in a small forested stream. We measured FA content of autochthonous food sources (aquatic primary producers = periphyton, green algae, red algae, bryophytes), allochthonous food resources (terrestrial matter = benthic and transported organic matter [BOM and TOM, respectively]), and macroinvertebrate consumers (Hydropsyche spp., Ephemerella spp., isopods, oligochaetes). We examined whether FAs could be used as trophic markers and tried to identify which food sources best provided macroinvertebrates with essential FAs (EFA, ω3 and ω6 groups). Primary producers consistently had greater content of several EFAs (18:2ω6 and 18:3ω3 in green algae, 20:5ω3 in diatoms, 20:4ω6 in bryophytes) than did terrestrial matter. The ratio of Σω3/Σω6 FAs, a putative marker of the relative amount of autochthonous vs allochthonous matter, was greatest in macroinvertebrates, followed by algae, and was significantly correlated with chlorophyll a content of food sources (periphyton, ultrafine BOM, and TOM). The seasonal dynamics of EFA content of BOM and TOM varied with particle size. Other FAs were identified as specific markers for diatoms (20:5ω3 [eicosapentaenoic acid], 16:1ω7, 16:ω4s, 16C-polyunsaturated FAa [PUFAa]), green algae (18:3ω3 [α-linolenic acid], 18:2ω6 [linoleic acid], 16C-PUFAb), and bryophytes (20:4ω6, 20:3ω3). Terrestrial matter had higher levels of bacterial and fungal FAs than did primary producers. Nonmetric multidimensional scaling analyses based on FA spectra of foodweb components in early spring (open canopy) and mid-summer (shaded canopy) confirmed that Ephemerella and Hydropsyche consumed mainly autochthonous food sources, even during the shaded summer period. Isopods and oligochaetes consumed a mixed diet of terrestrial matter and algae. Autochthonous food sources may be a more important part of the diets of benthic macroinvertebrates in forested streams than previously recognized.

Accumulation of heavy metals by aquatic mosses. 2: Rhynchostegium riparioides

A study was made of general ecology and metal accumulation in the widespread aquatic moss Rhynchostegium riparioides, (Hedw.) C. Jens. with a view to developing the use of this species as a monitor of heavy metal pollution. In order to establish a data bank for statistical analysis, samples of water and moss were taken within a 6-week period from 105 sites (10-m reaches) in Northern England from streams and rivers of diverse physical and chemical types. Analyses were made of 14 metals (Na, Mg, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Ba, Pb) in both 2-cm tips and whole plants. The same 14 metals were also measured in both total and filtrable water, together with 12 other variables. Samples of tips were easier to prepare for analysis, but had significantly (p < 0.001) lower concentrations of all metals except Na and K. Significant correlations (p < 0.001) between metal in moss and aqueous metal were found for ten metals (Na, K, Mg, Ca, Mn, Cu, Zn, Cd, Ba, Pb). Correlations between metals in moss and in water were in general similar for tips and whole plants, but much higher for tips with Na, Zn and Cd; the relationship was quite similar whether total or filtrable water was considered, with the exception of Ba where the correlation was much higher with the latter. A multiple regression was used to suggest which variables in water and/ or moss may influence accumulation of Co, Ni, Cu, Zn, Cd, Ba and Pb in the moss. For instance, the variables which had a very highly significant effect on Pb in tips were Pb, filtrable reactive phosphate and Zn in the water. A discussion is included of how the data may be used for monitoring purposes.

Effect of Vallisneria americana (L.) on community structure and ecosystem function in lake mesocosms

Submerged aquatic vegetation is known as a key structural component and regulator in ecosystems. In this mesocosm study, we examine community- and system-level responses to the presence of Vallisneria americana (L), a deep-rooted macrophyte. Phytoplankton, bacteria and filamentous algal biomasses were significantly lowered in the presence of V. americana. In addition, mesocosms with macrophytes had significantly reduced porewater phosphate and iron, water column dissolved organic carbon and total suspended solids, but elevated sediment redox. All mesocosms were net autotrophic (gross primary production/respiration >1). Compared to the macrophyte treatments, the control mesocosms had lower diel net primary production (NPP) midway through the experiment (d 16), but at the end of the experiment (d 36), the controls had the higher values, presumably due to increased filamentous algae. NPP and NPP/R were constant in the macrophyte treatments, whereas NPP/R increased significantly from middle to end of the experiment in the controls. We show that community and system-level responses to the presence of V. americana have significant consequences on system structure and function.

Influence of Three Contrasting Detrital Carbon Sources on Planktonic Bacterial Metabolism in a Mesotrophic Lake

A bstractLakes receive organic carbon from a diversity of sources which vary in their contribution to planktonic microbial food webs. We conducted a mesocosm study to test the effects of three different detrital carbon sources (algae, aquatic macrophytes, terrestrial leaves) on several measures of microbial metabolism in a small meso-eutrophic lake (DOC ≈ 5 mg/L). Small DOC additions (ΔC < 1 mg/L) affected bacterial numbers, growth, and pathways of carbon acquisition. Macrophyte and leaf detritus significantly increased TDP and color, but bacterial densities initially (+12 h) were unaffected. After 168 h, densities in systems amended with terrestrial detritus were 60% less than in controls, while production rates in mesocosms with macrophyte detritus were 4-fold greater. Detritus treatments resulted in greater per-cell production rates either through stable cell numbers and greater growth rates (macrophyte-C) or lower densities with stable production rates (terrestrial-C). After only 12 h, rates of leucine aminopeptidase (LAPase) activity were 2.5× greater in macrophyte-C systems than in controls, but LAPase and β-N-acetylglucosamindase activities in systems amended with terrestrial-C were only 50% of rates in controls. After 168 h, β-xylosidase rates were significantly greater in communities with terrestrial and phytoplankton detritus. Microbial utilization of >20% of 102 carbon sources tested were affected by at least one detritus addition. Macrophyte-C had positive (6% of substrates) and negative (14%) effects on substrate use; terrestrial detritus had mainly positive effects. An ordination based on carbon-use profiles (+12 h) revealed a cluster of macrophyte-amended communities with greater use of psicose, lactulose, and succinamic acid; controls and algal-detritus systems were more effective in metabolizing two common sugars and cellobiose. After 168 h, communities receiving terrestrial detritus were most tightly clustered, exhibiting greater use of raffinose, pyroglutamic acid, and sebacic acid. Results suggest that pelagic bacterial communities respond to changes in organic carbon source rapidly and by different routes, including shifts in per-cell production rates and variations in degradation of a variety of compounds comprising the DOC pool.

Are net-spinning caddisflies what they eat? An investigation using controlled diets and fatty acids

Abstract Polyunsaturated fatty acids (PUFAs) are abundant in stream-dwelling aquatic insects and might be essential for their growth and survival. We conducted a controlled study designed to clarify fatty acid (FA) assimilation and metabolism by net-spinning caddisfly larvae (Hydropsyche sp.). Specifically, our goal was to determine if these insects could synthesize essential FAs (18:2ω6, 18:3ω3, 20:4ω6, and 20:5ω3) de novo or elongate them from precursors, or if they must acquire them from their diet. In laboratory experiments, we supplied controlled diets (commercial fish food, oat particles, Cladophora glomerata, and conditioned leaves) to larvae in individual microcosms that simulated stream conditions. Caddisfly FA profiles consistently matched those of the diets provided, and in general, these insects had very limited abilities to synthesize and elongate essential FAs. Concentrations of linoleic (18:2ω6) and linolenic (18:3ω3) acid declined significantly in caddisflies fed diets depleted in these FAs. To test the ability to elongate FAs, caddisflies were fed a diet depleted in arachidonic acid (20:4ω6), but rich in its precursor 18:2ω6. Tissue concentrations of 20:4ω6 declined, suggesting that the ability of caddis larvae to elongate 18:2ω6 to 20:4ω6 is limited or absent. Caddisflies accumulated 20:5ω3 at greater assimilation efficiencies than for any other FA, suggesting a key importance of this FA. Across all experiments, caddisflies gained mass, total FA content, or both when supplied with all food sources except leaf litter. We suggest that caddisflies in streams must obtain essential FAs either from algal material or from predation.

Accumulation of heavy metals by aquatic mosses. 3: Seasonal changes

AbstractThe changes taking place at seven stream and river sites over a 14-month period were followed for the following:1)% cover of Rhynchostegium riparioides;2)relative abundance of Rhynchostegium as part of the whole plant community and, where present, also Amblystegium riparium and Fontinalis antipyretica;3)18 water chemistry variables;4)concentrations of nine metals in 2-cm tips of Rhynchostegium at all sites and of Amblystegium and Fontinalis at one site each. A decrease in the amounts of these mosses occurred in winter at most sites, the effect being most pronounced with Amblystegium. Nevertheless the majority of plants which remained had healthy shoots suitable for sampling for metal analysis at all times of year. There were marked temporal changes in the concentrations of metals in the 2-cm tips at each site, but few of these appeared to be related to seasonal events. The most plausible was for Pb in Rhynchostegium at a main river site, where increased accumulation in winter was probably an indirect effect of other chemical differences in the water during a period of high flows. Provided healthy shoots were available, there was no indication of seasonal differences in metal accumulation resulting from features of the mosses themselves.

Predominance of picoplankton and nanoplankton in eutrophic Calder Lake

A study was conducted to examine factors regulating the biomass of algal picoplankton in Calder Lake, a small eutrophic lake in southern New York state. A particular focus was a current paradigm which suggests that larger cells may dominate in nutrient-rich waters, while smaller cells may predominate only in oligotrophic waters. Over two years, phytoplankton biomass consisted predominantly (74% on average) of very small organisms; nanoplankton (<20 to 2 µm: 39%) and picoplankton (<2 µm to 0.2 µm: 35%), despite the presence of surface blooms of colonial cyanobacteria (Microcystis aeruginosa, Anabaena limnetica), and dense metalimnetic populations of the dinoflagellate Ceratium hirundinella. This dimictic system is characterized by relatively high levels of total P (max = 85, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiEayaara% aaaa!3702!\[\bar x\] = 9.7 µg P/L), inorganic P (max = 26, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiEayaara% aaaa!3702!\[\bar x\] = 4.5 µg P/L), and total inorganic N (max = 285, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiEayaara% aaaa!3702!\[\bar x\] = 85 µg P/L), but larger forms were rarely the most abundant. Unlike some marine systems, greater abundance of algal picoplankton was not associated with deeper strata (low light), or warmer temperatures. Data suggest that midsummer nutrient limitation, especially P-limitation, favors the development of pico- and nanoplankton in the limnetic zone of eutrophic lakes.

Strong Indirect Effects of a Submersed Aquatic Macrophyte, Vallisneria americana, on Bacterioplankton Densities in a Mesotrophic Lake

Phytoplankton and allochthonous matter are important sources of dissolved organic carbon (DOC) for planktonic bacteria in aquatic ecosystems. But in small temperate lakes, aquatic macrophytes may also be an important source of DOC, as well as a source or sink for inorganic nutrients. We conducted micro- and mesocosm studies to investigate the possible effects of an actively growing macrophyte, Vallisneria americana, on bacterial growth and water chemistry in mesotrophic Calder Lake. A first microcosm (1 L) study conducted under high ambient NH4+ levels (NH4+ ≥ 10 µM) demonstrated that macrophytes had a positive effect on bacterial densities through release of DOC and P. A second microcosm experiment, conducted under NH4+-depleted conditions (NH4+ < 10 µM), examined interactive effects of macrophytes and their sediments on bacterial growth and water chemistry. Non-rooted macrophytes had negative effects on bacterial numbers, while rooted macrophytes had no significant effects, despite significant increases in DOC and P. A 70-L mesocosm experiment manipulated macrophytes, as well as N and P supply under surplus NH4+ conditions (NH4+ ≥ 10 µM), and measured effects on bacterial growth, Chl a concentrations, and water chemistry. Bacterial growth and Chl a concentrations declined with macrophyte additions, while bacterial densities increased with P addition (with or without N). Results suggest that the submersed macrophyte Vallisneria exerts a strong but indirect effect on bacteria by modifying nutrient conditions and/or suppressing phytoplankton. Effects of living macrophytes differed with ambient nutrient conditions: under NH4+-surplus conditions, submersed macrophytes stimulated bacterioplankton through release of DOC or P, but in NH4+-depleted conditions, the influence of Vallisneria was negative or neutral. Effects of living macrophytes on planktonic bacteria were apparently mediated by the macrophytes use and/or release of nutrients, as well as through possible effects on phytoplankton production.

Hydrogen ion buffering of culture media for algae from moderately acidic, oligotrophic waters

Five hydrogen ion buffers were compared for their usefulness in regulating pH in a model oligotrophic, moderately acidic (pH 6.0) algal growth medium. These were 3,3‐dimethylglutaric acid (DMGA), tricarbaliylic acid (TCA), trans‐aconitic acid (tAA), N‐2‐hydroxyethylpiperazine‐N′‐2‐ethanesulfonic acid (HEPES) and 2‐(N‐morpholino) ethanesulfonic acid (MES). All buffers (2.5 mM) except HEPES limited the reduction of pH in a NH4+‐based medium during growth of Chrysochromulina breviturrita Nich. to less than 0.12 units, compared with more than 2 units in an unbuffered medium. Long term growth of C. breviturrita in these media was significantly inhibited (P < 0.05) by TCA and tAA. MES was able to control pH with the minimum amount of NaOH (1.0 mM) added to the medium to adjust to pH 6.0. Four of five bacterial isolates were capable of utilizing tAA as a sole organic‐C source, and no isolate could metabolize HEPES or MES. No significant differences (P > 0.05) were found in the maximum growth rates of six algal species (from five classes) in a medium with or without MES buffer, although significantly greater cell yields of Ochromonas danica Prings. were obtained in the buffered medium.