Algal Regulation of Extracellular Enzyme Activity in Stream Microbial Communities Associated with Inert Substrata and Detritus

We tested the hypothesis that algae influence the activities of extracellular enzymes involved in mineralization processes within microbial assemblages in streams. We tested the prediction that the factors that influence algal biomass and photosynthesis (i.e., diel fluctuations in photosynthetically active radiation [PAR], long-term variations in light regime, and community development stage) would have a corresponding effect on extracellular enzyme activities. We also tested the prediction that algae would influence enzyme activities on inorganic substrata and in detrital communities where they ultimately would influence plant litter decomposition rates. We allowed microbial communities to develop on inert substrata (glass-fiber filters) or on leaf litter in artificial streamside channels. For each community type, we examined the effects of long-term light manipulations, community development stage, and diel periodicity on the activities of P-glucosidase, alkaline phosphatase, leucine-aminopeptidase, and phenol oxidase. In addition, we measured the decomposition rates of the leaf litter substrata in the low- and high-light treatments. Our results support the prediction that factors that influence algal photosynthesis and biomass in the short (diel fluctuations in PAR) and long (shading, community development stage) term ultimately influence enzyme activities in microbial communities associated with both inorganic substrata and detritus. Furthermore, decomposition rates of organic detritus probably are enhanced by algal colonization and activity. Algal photosynthesis might enhance redox and pH conditions within microbial communities, and in turn, might increase the activities of oxidative and hydrolytic enzymes. As a consequence, photoautotrophic activities might stimulate heterotrophic pathways in stream ecosystems by creating conditions favorable for decomposition of both dissolved and particulate organic detritus

Alteration of Microbial Communities Colonizing Leaf Litter in a Temperate Woodland Stream by Growth of Trees Under Conditions of Elevated Atmospheric CO\u3csub\u3e2\u3c/sub\u3e

Elevated atmospheric CO2 can cause increased carbon fixation and altered foliar chemical composition in a variety of plants, which has the potential to impact forested headwater streams because they are detritus-based ecosystems that rely on leaf litter as their primary source of organic carbon. Fungi and bacteria play key roles in the entry of terrestrial carbon into aquatic food webs, as they decompose leaf litter and serve as a source of nutrition for invertebrate consumers. This study tested the hypothesis that changes in leaf chemistry caused by elevated atmospheric CO2 would result in changes in the size and composition of microbial communities colonizing leaves in a woodland stream. Three tree species, Populus tremuloides, Salix alba, and Acer saccharum, were grown under ambient (360 ppm) or elevated (720 ppm) CO2, and their leaves were incubated in a woodland stream. Elevated-CO2 treatment resulted in significant increases in the phenolic and tannin contents and C/N ratios of leaves. Microbial effects, which occurred only for P. tremuloides leaves, included decreased fungal biomass and decreased bacterial counts. Analysis of fungal and bacterial communities on P. tremuloides leaves via terminal restriction fragment length polymorphism (T-RFLP) and clone library sequencing revealed that fungal community composition was mostly unchanged by the elevated-CO2 treatment, whereas bacterial communities showed a significant shift in composition and a significant increase in diversity. Specific changes in bacterial communities included increased numbers of alphaproteobacterial and cytophaga-flavobacter-bacteroides (CFB) group sequences and decreased numbers of betaproteobacterial and firmicutes sequences, as well as a pronounced decrease in overall Gram-positive bacterial sequences

Comparing Effects of Nutrients on Algal Biomass in Streams in Two Regions with Different Disturbance Regimes and with Applications for Developing Nutrient Criteria

Responses of stream algal biomass to nutrient enrichment were studied in two regions where differences in hydrologic variability cause great differences in herbivory. Around northwestern Kentucky (KY) hydrologic variability constrains invertebrate biomass and their effects on algae, but hydrologic stability in Michigan (MI) streams permits accrual of high herbivore densities and herbivory of benthic algae. Multiple indicators of algal biomass and nutrient availability were measured in 104 streams with repeated sampling at each site over a 2−month period. Many measures of algal biomass and nutrient availability were positively correlated in both regions, however the amount of variation explained varied with measures of biomass and nutrient concentration and with region. Indicators of diatom biomass were higher in KY than MI, but were not related to nutrient concentrations in either region. Chl   a and % area of substratum covered by Cladophora were positively correlated to nutrient concentrations in both regions. Cladophora responded significantly more to nutrients in MI than KY. Total phosphorus (TP) and total nitrogen (TN) explained similar amounts of variation in algal biomass, and not significantly more variation in biomass than dissolved nutrient concentrations. Low N:P ratios in the benthic algae indicated N as well as P may be limiting their accrual. Most observed responses in benthic algal biomass occurred in nutrient concentrations between 10 and 30 μg TP  l −1 and between 400 and 1000 μg TN l −1 .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42905/1/10750_2005_Article_1611.pd

Emerging Data on Link between Acid Mine Drainage and Nutrient Processing

Stream ecosystems provide a myriad of important services to humans. Examples include providing clean drinking water for municipalities, detoxifying pesticides, and offering recreational fishing opportunities. One often overlooked “ecosystem service”, however, is the processing and retention of excess phosphorus and nitrogen from sewage and agricultural runoff. The ability of small streams to process and retain nitrogen and phosphorus has important implications for the greater Susquehanna River watershed and ultimately the health of Chesapeake Bay. In healthy streams, bottom-dwelling microorganisms actively remove nitrogen and phosphorous from the water and transfer it up the food chain before recycling it back into the water where it is displaced downstream. This process slows the downstream progression of nitrogen and phosphorous and consequently decreases nutrient loading rates to large bodies of water, such as Chesapeake Bay. However, impairments such as acid mine drainage (AMD) might interfere with a stream’s ability to retain these nutrients. Our current research focuses on how AMD in the upper Susquehanna River basin might impair normal stream functions, such as nutrient retention, and how this might contribute to the nutrient loading problem to Chesapeake Bay. Furthermore, we are investigating the effectiveness of AMD remediation efforts in restoring this vital ecosystem service. Preliminary results suggest that the microbial communities involved in stream nutrient dynamics and nitrogen retention are seriously impaired by AMD. However, much more work needs to be completed before we fully understand the effects of AMD on nutrient retention in streams and the ultimate implications for nutrient loading to Chesapeake Bay

Stream Size Determines the Response of Microbial Communities to Phosphorus Pulses During Storm Runoff

Brief phosphorus (P) pulses associated with storm runoff have the potential to be important drivers of microbial community growth in stream ecosystems. We measured the capacity of stream microbial communities to respond to brief P pulse during natural storm events in a small headwater tributary of Fishing Creek and a larger fifth order section near Bloomsburg, PA. Storm runoff in the fifth order section of Fishing Creek resulted in substantial increases in algal polyphosphate, the primary P storage structure for microorganisms. P storage in this reach appeared to be followed by a period of rapid growth. In contrast, we did not observe such an increase in polyphosphates in the headwater section of Fishing Creek for natural storm runoff events or after we performed an artificial P release. Our results indicate that the combination algae domination of the microbial community and P pulses that are higher in concentration and duration might allow P delivered during storm runoff to have greater ecosystem-level effects in larger streams and rivers

A Crayfish Survey of the Fishing Creek Watershed in Northeastern Pennsylvania

Introductions of invasive crayfish species have impacted freshwater ecosystems worldwide, typically resulting in displacement of native crayfish species by non-native species. Two crayfish species (Orconectes limosus and Cambarus bartonii) are thought to be native to the Susquehanna River Drainage in eastern and central Pennsylvania. However, several non-native crayfish (e.g., O. obscurus, O. rusticus, O. virilus) have been introduced and have become established in this river system. Few data are available on the present occurrence and distribution of crayfish species within the Fishing Creek watershed, a drainage encompassing approximately 620 km2 within the North Branch Susquehanna River Drainage in eastern Pennsylvania. Records from the early 1900s report the occurrence of both O. limosus and C. bartonii in this watershed; however, recent point-surveys in the lower reaches of the watershed have reported the presence of the non-native crayfish Orconectes obscurus. In this work, crayfish were sampled at fifteen sites from the lower reaches of Fishing Creek to its headwater branches and major tributaries in order to elucidate the current presence and distribution of crayfish species within this watershed. A total of 484 crayfish were collected, representing the species O. obscurus (n = 376) and C. bartonii (n = 108). O. obscurus were found to be widespread within the drainage, but absent from the upper reaches of the Fishing Creek watershed, potentially as a result of physical or environmental barriers (e.g., dams, shifting stream characteristics). C. bartonii were primarily distributed in the upper portions of the Fishing Creek watershed, but also found in smaller tributary near the mouth, and sympatric (but in found in low abundance) with O. obscurus in the central portions of the drainage. This distribution of C. bartonii within the watershed is likely due to habitat preferences (e.g., cooler, smaller, and higher gradient portions of streams) of this species, but may also result from displacement by O. obscurus. The historically present O. limosus was not collected within the watershed, potentially suggesting local extirpation via competition with O. obscurus, as has been reported in other elsewhere in aquatic ecosystems invaded by non-native congeners

Polyphosphate Storage Dynamics Across a Gradient of Phosphorous Enrichment

Accurately assessing how algal-dominated biofilms in streams respond to anthropogenic phosphorous enrichment is crucial for ensuring sustainable agricultural land use. Understanding phosphorous storage dynamics particularly in the form of polyphosphate can assist in creating more effective nutrient criteria. The purpose of this study is to examine polyphosphate storage dynamics across a gradient of agricultural impairment in 19 Pennsylvania streams. This study sought to determine the quantity of Polyphosphate stored in response to phosphorous availability. Results indicate biofilms are able to store polyphosphate in both low and high concentration SRP streams. These results may give evidence to support both the “overplus” response and the “luxury” response at both ends of the phosphorous gradien

Response of Stream Biofilms to Pulsed Versus Steady-State Phosphorus Additions

Our current understanding of how algal-dominate biofilms in streams respond to phosphorus (P) enrichment is largely based on the assumption that streams have a constant P supply. However, in reality natural streams experience large swings in P concentrations due to runoff and in-stream biotic and abiotic uptake. The purpose of this study was to compare the effects of a steady-state P release versus successive pulse events on algae-dominated biofilms colonizing artificial streams. One treatment (n=4) was maintained at a constant 12 µg P/L, another was subjected to weekly 8 h pulses at 252 µg P/L (n=4) and a third treatment was maintained below P detection limits (n=4). Both the steady-state and the pulse treatments received an equivalent amount of P by the end of the experiment. Preliminary pulse amplitude modulation fluorometry data indicate that algae treated with the phosphorous pulse had a greater photosynthetic capacity and ability to utilize the phosphorus

Understanding the Environmental Context of Algal Priming of Coarse Particulate Organic Matter Decomposition in Streams

Streams can obtain energy from two main sources: autochthonous organic matter or allochthonous inputs of organic matter. Interactions between organisms involved in these two types of energy acquisition can exist within biofilms. Biofilms are microcommunities of algae, fungi, bacteria, and protozoa that form on inert and organic substrata. Previous experiments have observed interactions between photosynthetic and heterotrophic organisms within biofilms in a process called algal priming. The release of a labile carbon source by algae may stimulate the decomposition of coarse particulate organic matter by heterotrophic organisms. To better understand algal priming, we evaluated the environmental factors that may influence the process within biofilms. Presence of light, nutrients, and a labile carbon source were manipulated using shading and chemical diffusing substrata. Unbleached cotton strips were attached to clay saucers containing the chemical diffusing substrata that was manipulated into four treatments: a control, the addition of nutrients, the addition of a labile carbon source, and the addition of both nutrients and a labile carbon source. The clay saucers were attached to a tile and placed in a stream under a transparent or darkened shade. After one week, cotton strips were collected and tested for respiration and tensile strength which is a measure of decomposition. Flooding prevented further sample collection beyond one week. A future study will involve placing cotton strips within transparent or darkened tubes into 25 streams of varying stream order and nutrient content. After one month, the cotton strips will be collected and evaluated for decomposition, algal biomass, bacterial biomass, fungal biomass, extracellular enzyme activity, and respiration. In examining environmental context, we aim to provide information to better understand the role priming may play in the cycling of carbon within streams