Amelia K. Ward

NOSTOC (CYANOPHYTA) PRODUCTIVITY IN OREGON STREAM ECOSYSTEMS: INVERTEBRATE INFLUENCES AND DIFFERENCES BETWEEN MORPHOLOGICAL TYPES1

Nostoc parmelioides colonies housing dipteran larvae (Cricotopus) had higher rates of weight specific photosynthesis than colonies without the larvae. A change in colony shape, which allowed the alga to be exposed to higher light intensities, occurred, in the presence of the larvae. This change in morphology together with potential nutrient additions by the larvae and other effects may have caused the increase in photosynthetic rates. Nostoc colonies were typically found in open areas of small streams in western Oregon mountains where the ability to respond to high light would be advantageous in supporting the metabolically expensive process of nitrogen fixation.

4 – GULF COAST RIVERS OF THE SOUTHEASTERN UNITED STATES

The river basins of the eastern Gulf Coast lie west of the Atlantic slope and east of the Mississippi River. The region has abundant water resources, including seven major rivers that arise and flow through five physiographic provinces in five states to empty into the Gulf of Mexico. These rivers vary widely in size, hydrology, geomorphology, and water chemistry, but experience a similar climate and exhibit many biological similarities. The dominant physiographic province through which the rivers flow is the coastal plain, more specifically, the sections named the eastern Gulf Coastal Plain and the Floridan. There are five freshwater ecoregions within the eastern Gulf of Mexico region, arranged by longitude. These include portions of the Mississippi Embayment and Florida ecoregions, all of the Mobile Bay and Apalachicola ecoregions, and much of the Florida Gulf ecoregion. Two of these, the Mobile Bay and the Apalachicola, follow watershed boundaries of the Mobile and Apalachicola river basins, whereas the remaining three ecoregions include multiple river basins. All rivers in this region flow from north to south into the Gulf of Mexico, and all are located between 84°W and 91°W longitude and 30°N and 35°N latitude. The eastern Gulf Coast rivers encompass a rich variety of aquatic habitats and resources. This diversity is most evident in the fishes, mollusks, crayfishes, and caddisflies.

Inorganic nitrogen regimes in an Alabama wetland

We measured spatial and temporal patterns of inorganic nitrogen (Ni) concentrations and fluxes in surface water flowing into, within, and leaving an Alabama wetland between January 1993 and November 1994. Nutrient concentrations were extremely variable both spatially and temporally and NH4-N accounted for 75-98% of all Ni. The wetland was a sink for NO3-N, because concentration and total mass were consistently lower in the stream downgradient from the wetland than at the upstream site. In contrast, NH4-N concentrations increased downstream on 15 of the 23 sampling dates, although reduced discharge out of the wetland often resulted in a net retention of NH4-N. Within the wetland, concentrations of Ni were low and relatively homogeneous among sites during cool, high-flow periods. During low-flow periods, NH4-N concentrations and site-to-site variance increased. Episodic increases in NH4-N concentrations were common in marsh areas, but nutrient pulses were dampened at downgradient open-pond sites. Porewater had significantly more Ni than surface water and was also dominated by NH4-N (often >1000 μg/L). Interstitial concentration gradients resulted in diffusive transport of NH4-N to the surface, and likely contributed to transient increases in NH4-N concentration in marsh habitats. Removal of Ni added to benthic chambers in the open pond was extremely rapid; 550-600 μg N/L were removed from the water column in 24-48 h. Although potential uptake rates were rapid, actual rates appear to be insufficient to cause the wetland to be a consistent N trap over time; the Talladega Wetland Ecosystem may vary from a net Ni-sink to an Ni-source at different times of the year or from 1 year to the next.

BLUE‐GREEN ALGAL MATS IN A SMALL STREAM1

Bedrock erosional features in a small stream (Little Schultz Creek, Bibb County, Alabama) created a variety of habitats for epilithic growth. One suck habitat was illustrated by the occurrence of small falls (<0.3 m) in the main channel of the stream and blue‐green algal mats associated with them. The cohesive, laminar algal mats were found at 15 such sites along a 250‐m reach of the stream. The primary mat matrix consisted of the blue‐green alga Oscillatoria submembranacea Ardissone and Strafforella. The uppermost portion of each mat consisted of a thin (<1 mm thick) green layer of biologically active filaments. The lower layers were thicker (up to 2 cm thick) and consisted of brown laminae of Oscillatoria filaments, and associated sediments. In addition, numerous diatoms mere associated with the mat surface. Some were loosely attached (e.g. Achnanthes); others (Cymbella tumida (Bréb.) V. H.) were stalked. These mats were present throughout the year and showed a bimodal annual distribution with maxima hi February and July. In February, total mat coverage was higher than in July. This winter maximum may have been related to a mode of growth dependent upon sedimentation from storm events and subsequent upward growth of the alga. Mat primary productivity on an areal basis (432 mg C · m−2· d−1 in March and 907 mg C · M−2· d−1 in April) was 2–12 times the maxima measured on epizoic and cobbles surfaces and other bedrock surfaces in the same stream. The limited areal coverage of the mats, when compared to other surfaces available for algal colonization, made them less important than other epilithic and epizoic surfaces in terms of total primary production in this stream reach. However, we propose that the combination of their unique structure and high primary productivity may make these algal mats sites of high algal and bacterial metabolic activity, which may include anaerobic processes in midchannel, where such activity would not be expected to occur.

SODIUM: SOME EFFECTS ON BLUEGREEN ALGAL GROWTH1

The growth of heterocystous bluegreen algae in various concentrations of sodium, was examined in axenic culture as well as in situ studies. Anabaena cylindrica Lemm. with no Na+ added, suffered from decreased rates of acetylene reduction, 14C, assimilation, excretion of organic C as well as lower concentrations of chlorophyll a and particulate organic C compared to cultures supplied with 5, 10, and 50 mg Na+·l−1 Sodium deficient algae released, extracellularly a higher percentage of previously fixed C as organic C. No differences in any parameter measured were demonstrable among cultures grown with 5, 10, and 50 mg Na+·l−1 High nitrate concentrations (20 mg NO3−·l−1) resulted in decreased rates of acetylene reduction and heterocyst numbers in. Na sufficient, and Na deficient cultures: however, decreased, cellular Na content at high NO3− levels occurred only in N deficient, cultures. Higher percentages of excreted organic C occurred with increasing NO3− concentrations in Na deficient cultures. Sodium enrichment of natural bluegreen populations with the addition of 50, 100, and 200 mg Na+·l−1 elicited neither a stimulatory nor an inhibitory response in photosynthetic C fixation. In contrast, the addition of small amounts of Na+ (5 mg·l−) resulted in increased C fixation. However, since the Na. concentration of the lake water, at ca. 5 mg Na+·l−1, was sufficient for growth of the bluegreens present, sodium, is not assumed to be limiting under most natural conditions. No increase in in situ acetylene reduction rates occurred with additions of sodium.

QUALITATIVE AND QUANTITATIVE OBSERVATIONS ON AQUATIC ALGAL COMMUNITIES AND RECOLONIZATION WITHIN THE BLAST ZONE OF MT. ST. HELENS, 1980 AND 19811

Despite the destruction and total rearrangement of much of the area north of Mt St. Helens, many different species of algae became established in the aquatic systems located in the blast zone within 3–4 months after the eruption of May 18, 1980. Initial sites of intense algal activity were found in benthic regions associated with warm springs and in the littoral and phytoplanktonic communities of some small lakes. In the summers of 1980–81, overall phytoplankton numbers and activity were low in the large lakes closest to the crater (e.g. Spirit Lake). However, diatoms, blue‐green and green algal isolates from these lakes were obtained in laboratory cultures on a reduced inorganic medium used to enumerate metal and sulfur oxidizing bacteria. Species of Nodularia, Pseudanabaena, Anabaena, Oscillatoria, Nitzschia, Tribonema, Chlamydomonas, Chlorella, and microflagellates (predominantly cryptomonads) were among the more common forms found in preserved samples or isolated in cultures.

Differential incorporation of algae and bacteria by Elimia clara (Prosobranchia:Pleuroceridae)—a study using dual-labeled epilithon

The study of snail herbivory has typically stressed the importance of autotrophic components in periphyton to snail nutrition despite growing evidence of the role of microbial food webs, specifically the roles of heterotrophic bacteria as a food resource to higher trophic levels. Snails of the family Pleuroceridae are the most dominant and ubiquitous grazers found among small, low-order, carbonate streams in the Valley and Ridge physiographic province of Alabama. Two snail species, Elimia clara and E. cahawbensis, co-inhabit Little Schultz Creek, which is in this region. The former is more abundant than the latter and frequently occurs in erosional sites with rapid current. Past studies have shown that E. clara ingests periphyton scraped from bedrock and cobble substrata as a food source. The main objective of this study was to determine if E. clara differentially incorporates bacteria or algae from the epilithic material. The microbial community attached to bedrock was dual-labeled with 14C-NaHCO3 and 3H-thymidine for the algal and bacterial components, respectively, and exposed for measured time periods to snail grazers. An electivity index (D) was calculated using snail weight-specific radioisotope incorporation and radioisotope availability in the epilithon. An index value of +1 indicated incorporation of primarily bacterial biomass, whereas a value of −1 indicated primarily algal incorporation by snails. A 0 value indicated no preference for either food type with equal incorporation of both. Two separate experiments yielded mean index values of −0.18 and −0.22, suggesting that E. clara assimilated both bacterial and algal material but with slightly more incorporation of algae.

Geological Mediation of Stream Flow and Sediment and Solute Loading to Stream Ecosystems Due to Climate Change

The effects of global warming and predicted widespread changes in climate within the next century caused by the “greenhouse effect” have been the subject of much scientific debate. Research based on instrument records and indirect effects of climatic change, e.g., sea levels and ice cores, indicate that millennial changes in global temperatures fall roughly within an interval of ±1°C. However, “greenhouse models” responding to the doubling of CO2 (0.06%), which is predicted to occur within the next century, indicate that global temperatures may increase by approximately 3°C (Hansen et al., 1981; Mearns et al., 1990). The “greenhouse models” have been severely criticized for emphasizing positive feedbacks (warming phenomena) within the atmospheric-oceanic system at the expense of negative feedbacks (cooling phenomena) (Reifsnyder, 1989; Lindzen, 1990). Despite these criticisms, the reality of significant anthropogenic influence on atmospheric chemistry such as the documented increases in CO2 levels (e.g., Bascatow and Bjorkstrom, 1981) as well as the possibility for climatic changes related to “greenhouse gas” increases have initiated a high level of concern.

Ecology of Pectinatella magnifica (Bryozoa) in an Alabama oxbow lake: colony growth and association with algae

Colonies of the bryozoan Pectinatella magnifica commonly occur on submersed substrata in an oxbow lake (Touson Lake) in the floodplain of the Black Warrior River, Alabama. Seasonal growth patterns, substratum preference, and potential effects of bryozoan colonies on algal assemblages attached to artificial and natural substrata were determined. Colony growth on artificial substrata (pine sticks) and natural ones (dead cypress twigs and aquatic plants) was monitored at biweekly intervals from the appearance of bryozoans during early autumn to the loss of colonies from substrata in late December. Maximum colony growth occurred during late September and early October. Some colonies reached up to 65 cm in length and 10 cm in diameter. Colonies showed no preference among the substrata examined, but young colonies always developed first on the shaded side of the substratum. The presence of bryozoan colonies affected the composition of attached algae. Blue-green algae (90%) dominated on surfaces enclosed by the colonies and also within the gelatinous colony matrix, whereas surfaces uncolonized by Bryozoa developed mixed communities of diatoms (78%), blue-green algae (12%), and green algae (11%).

Distribution and primary productivity of the epizoic macroalga Boldia erythrosiphon (Rhodophyta) in a small Alabama stream

The contribution of autochthonous carbon to a small stream by the epizoic red macroalga Boldia erythrosiphon was determined from December 1985 through April 1986 in Little Schultz Creek, Alabama. Boldia grew almost exclusively on the snail species Elimia clara and E. cahawbensis. A mean of 323 snails/m2 was found in the stream, 49% of which had the alga attached. Elimia clara was nearly four times as abundant as E. cahawbensis and Boldia was significantly more associated with the former than with the latter snail. The differential distribution of the alga may be due to behavioral differences, E. clara preferring erosional sites with higher current rather than depositional sites. Boldia on snails contributed a mean of 37 mg C m-2 d-1 from January through April 1986 and a total of nearly 2 g C/m2 for the season. The latter value is one third of the seasonal primary production of epilithic algae on cobble measured in a previous study, and, when added to it, changes the annual pattern of autochthonous production in this stream. The productivity of the macroalga illustrates the importance of animals in providing substrata for algae in streams. In addition to the presence of snails, a combination of factors including total light input, the chemical nature of substrata, differential grazing pressure, and substratum availability may affect colonization and growth of Boldia.