Small Estuary Research Articles

Experimental evaluation of biases associated with sampling estuarine fishes with seines

Beach seines are widely used to estimate the density and species richness of fishes in estuaries. We evaluated the causes and extent of bias in estimates from seines using a series of field experiments in small estuaries in southern California, USA. Seining in spatially paired areas that were either enclosed by block nets or not, revealed that seines used without block nets underestimated density by more than 4-fold and species richness by more than 2-fold relative to blocked areas. Seining in paired blocked areas with seines of two lengths revealed that net length affected estimates of density, but not species richness; a 7.6-m long seine produced 1.6-fold higher estimates of total density than did a 15.2-m long seine due to increased catches of demersal fishes, but not midwater species. Paired sampling in blocked areas also revealed that many fishes initially evaded capture by the seine. Estimates of density but not species richness were significantly higher in areas through which a seine was swept 5 times compared to once. This was due to higher catches of demersal fishes but not midwater fishes in areas seined 5 times. Repeated seining through blocked areas revealed that the vast majority (90% or more) of species and individuals of midwater fishes were captured within the first 5 sweeps, compared to only about 50% of the individuals of demersal species. A mark-recapture study in blocked areas revealed lower probabilities of capture for demersal species relative to midwater species.

The green sturgeon and its environment: introduction

The green sturgeon, Acipenser medirostris, is one of two acipenserid fishes native to the temperate waters of the Pacific coast of North America. Originally, three species of sturgeon were described from this region, and this one named ‘‘medirostris’’ or ‘‘middle snout’’ based on the length of its rostrum relative to the other purported species (Ayers 1854), both of which were later determined to be white sturgeon, Acipenser transmontanus (Moyle 2002). The green sturgeon is similar in appearance to the congeneric white sturgeon, with which it cooccurs, except that its barbels are usually closer to the mouth than to the tip of the snout. Green sturgeon are heavily armored, possessing one dorsal, two lateral and two bottom rows of scutes or bony plates (Moyle 2002). In addition, there are often one or two large scutes behind the dorsal fin, as well as one behind the anal fin, which are both lacking in the white sturgeon. The common name of the species is apt due its distinctly olive-green body color, with olivaceous stripes usually present on its sides and ventral surface. Green sturgeon are currently thought to be comprised of two genetically distinct breeding populations (Israel et al. 2004): a northern distinct population segment (DPS) consisting of fish that spawn in the Rogue River, Oregon (Erickson et al. 2002), and the Klamath River, California (Van Eenennaam et al. 2001), and a southern DPS that spawns in the Sacramento River, California. Increasingly, many fish species are being recognized as consisting of multiple, genetically distinct stocks. In many cases, these stocks are managed separately because of distinctive phenotypic, physiological, and behavioral characteristics representative of the unique adaptations each stock has to the environmental conditions in a particular habitat (Waples 1995). Although little is known about what distinguishes these green sturgeon populations biologically, several unique physical characteristics differentiate the river systems in which they occur. Tidal flows in an expansive estuary, voluminous flows, long river length, and multiple tributaries in an extensive watershed distinguish the Sacramento River from the Rogue and Klamath Rivers with their small estuaries, relatively short length, and smaller watersheds. Based on the best information available to the National Marine Fisheries Service (Adams et al. in press), the southern DPS was A. P. Klimley (&) P. J. Allen J. T. Kelly Department of Wildlife, Fish & Conservation Biology, University of California, One Shields Avenue, Davis, CA 95616, USA e-mail: apklimley@ucdavis.edu

The distribution and abundance of the endangered Knysna seahorse Hippocampus capensis (Pisces: Syngnathidae) in South African estuaries

The occurrence, distribution and abundance of the endangered Knysna seahorse Hippocampus capensis in 10 estuaries on South Africa's warm temperate south coast, were investigated. Seahorses were found only in the Knysna, Swartvlei and Keurbooms estuaries. Sex ratios were even and, in most cases, more adults were found than juveniles. During the first year of study, seahorse densities were higher in the Swartvlei and Keurbooms estuaries than in the comparatively larger Knysna Estuary but, during the second year, seahorses were absent from the Keurbooms estuary, and the population size in the Swartvlei Estuary had decreased by more than 80%. These results suggest that, although the two smaller estuaries are able to support comparatively high densities of seahorses, population sizes may fluctuate considerably. Population size estimates for the Knysna Estuary were similar to those obtained in a previous study, suggesting that this estuary may represent a more stable environment and may thus be particularly important for the survival and conservation of this species.

Commentary

Mangroves in South Africa occur at one of the most southerly locations in the world, which provides a unique opportunity to study their dynamic responses to anthropogenic and natural perturbations. The exposed high-energy South African coastline restricts mangroves to 32 sheltered estuaries of which 18 (56%) are predominantly open to the sea. A large area of mangrove (47% of the country total) occurs in the uMhlathuze Estuary – a novel ecosystem formed by the creation of an artificial mouth. A Drivers-Pressures-State-Impacts-Response (DPSIR) framework was applied to understand factors of change and highlight governance and management responses. The largest mangrove area (440 ha) was lost during the construction of Durban Bay harbour. Mangroves (~7 ha) no longer occur in 10 small KwaZulu-Natal estuaries as a result of catchment and mouth disturbance. In the Eastern Cape, pressures are escalating in the form of harvesting for wood, cattle browsing and changes in mouth condition. Climate related warming and an increase in CO2 are positive conditions for mangroves to expand their distribution to higher latitudes but this will depend on propagule dispersal between estuaries and the availability of suitable habitats. Many of the small estuaries are temporarily closed to the sea for different periods thus limiting recruitment. An increase in the intensity of freshwater floods will scour banks and completely remove mangroves. It is important that these dynamic responses are understood and incorporated into management plans so that mangrove forests can be better protected and conserved.

High nutrient pulses, tidal mixing and biological response in a small California estuary: Variability in nutrient concentrations from decadal to hourly time scales

Elkhorn Slough is a small estuary in Central California, where nutrient inputs are dominated by runoff from agricultural row crops, a golf course, and residential development. We examined the variability in nutrient concentrations from decadal to hourly time scales in Elkhorn Slough to compare forcing by physical and biological factors. Hourly data were collected using in situ nitrate analyzers and water quality data sondes, and two decades of monthly monitoring data were analyzed. Nutrient concentrations increased from the mid 1970s to 1990s as pastures and woodlands were converted to row crops and population increased in the watershed. Climatic variability was also a significant factor controlling interannual nutrient variability, with higher nutrient concentrations during wet than drought years. Elkhorn Slough has a Mediterranean climate with dry and rainy seasons. Dissolved inorganic nitrogen (DIN) concentrations were relatively low (10–70 μmol L −1) during the dry season and high (20–160 μmol L −1) during the rainy season. Dissolved inorganic phosphorus (DIP) concentrations showed the inverse pattern, with higher concentrations during the dry season. Pulsed runoff events were a consistent feature controlling nitrate concentrations during the rainy season. Peak nitrate concentrations lagged runoff events by 1 to 6 days. Tidal exchange with Monterey Bay was also an important process controlling nutrient concentrations, particularly near the mouth of the Slough. Biological processes had the greatest effect on nitrate concentrations during the dry season and were less important during the rainy season. While primary production was enhanced by nutrient pulses, chlorophyll a concentrations were not. We believe that the generally weak biological response compared to the strong physical forcing in Elkhorn Slough occurred because the short residence time and tidal mixing rapidly diluted nutrient pulses.

Wind-generated tool marks resembling trace fossils in a shallow estuarine environment

A suite of tool marks were observed in the seaward section of a small estuary on the south coast of New South Wales. The marks were formed through wind-generated waves dragging Eucalyptus leaves and Casuarina fronds over the backshore sands that separate the closed estuary from the sea. Some of the marks formed through the process of tilting, which has not previously been recognised in an Australian setting. A number of the more complex marks closely resemble trace fossils left by fish, and differentiation between the two in the sedimentary record could be difficult. If correctly identified as tool marks, then they could give a spurious estimate of palaeoflow direction, as they correspond to the orientation of the prevailing winds at the time of formation. This study highlights the need for judicious interpretation of ambiguous grooves in the sedimentary record.

Observations of a Propagating Vortex in a Tidal Current

While observing the hydrodynamics and geomorphology of the entrance to Burrill Lake, a small estuary on the south coast of New South Wales, Australia, a striking vortex phenomenon was observed. This vortex is described and interpreted.

Flood discharges of a small river into open coastal waters: Plume traits and material fate

The dynamics of plumes from large rivers are relatively well known. Many estuaries are small, however, and discharge directly onto exposed, open shorelines and presumably produce smaller plumes that may have different properties. Therefore this study measured traits of a small estuary on the Australian East Coast as a model system, focusing on (a) plume size, (b) distinctness of plume edges, and (c) imprints on the seafloor. Although plumes were found to be limited in spatial extent (ca. 1 km offshore × 2.4 km longshore) and were constrained near the shore by onshore winds, they exported high nutrient loads from an urbanised watershed. The small plumes were shallow (<2 m) and strongly buoyant, with sharp vertical and horizontal clines similar to much larger plumes. The edges of the plumes were highly distinct, clearly separating disparate water masses that trapped significantly higher amounts of nutrients inside the plume. Some particulate material exported from the estuary in the plumes reached the benthos of the nearshore zone, as evidenced by increases in copper concentrations in sediments under the plume. By contrast, the amount of land-sourced carbon delivered by small plumes to the seafloor was minor in comparison to larger inputs from marine sources (e.g. onshore advection of phytoplankton blooms or algae dislodged from reefs) that swamped any contribution from plumes. Overall, small plumes can be important in land–ocean coupling, but their zone of influence may be limited.

On the award of TMS Honorary Membership, 26 November 2005 Professor John Murray – an appreciation

Abstract. Contrary to popular belief, Professor John Murray and Sir John Murray (of Challenger fame) are not one and the same person. To begin with, their careers are separated by almost a century, but our Professor John Murray (B.Sc., ARCS, Ph.D., DIC, D.Sc) is hardly less renowned in today’s world of micropalaeontology, especially with regards to ecological studies of the foraminifera.John William Murray was born in London in 1937. Most of his childhood was however spent in Bury (now Greater Manchester), having been evacuated in WW2, before he moved back to Worthing, Sussex, when he was 16. As a child he had been seriously interested in microscopy and geology, and therefore it was not surprising that when he went up to university, he chose to read Pure Geology at Imperial College, University of London, in 1956. There, someone showed him some foraminifera in a First Year practical and he hasn’t been able to keep away from them since! Not only did he get a First, but he won several prizes (the Murchison Medal, the Watts Medal and the Clement Le Neve Foster Prize) as well. On graduation he was offered the chance to undertake a Ph.D. in micropalaeontology, under David Carter. He chose to study the ecology of Recent foraminifera, which for the time was highly unusual. The result, a seasonal study of the living foraminifera of a small estuary (Christchurch Harbour, now in Dorset) was a seminal one. He was even kind enough, subsequently, to lend one of us . . .

Changes in biodiversity of the extremely polluted Golden Horn Estuary following the improvements in water quality

Long-term biological data supported by physicochemical parameters were evaluated to investigate the biodiversity of the Golden Horn Estuary from the past to the present. Limited observations dating back to 60 years ago indicated the existence of a diverse community in this small estuary. Unfortunately, in parallel with the increase in unplanned settlements and industry around the Golden Horn, pollution stress increased since the 1960s. Preliminary studies in the 1990s indicated survival of only a couple of pollution-resistant species, in the relatively cleaner lower estuary. Following the intensification of rehabilitation studies in 1998 and particularly after the opening of the floating bridge at the mid estuary; a remarkable day-by-day recovery in marine life has begun with the improving water quality. Nutrient concentrations decreased markedly; while water clarity significantly increased. Fecal coliform values decreased 10 3 fold. Phytoplankton composition changed and dense blooms of eukaryotic phytoplankters frequently occurred. Hydrogen sulfide almost completely disappeared even during the warmest periods of the year and dissolved oxygen concentrations increased. All results clearly depicted that the Golden Horn ecosystem shifted to eutrophic conditions from an anoxic environment. SCUBA dives in 2002, documented the level of diversification of life in the Golden Horn. All appropriate substratums were intensely covered by macrobenthic forms until the Halic Bridge and filter feeders dominated the plankton-rich ecosystem. Achieving the diversity of 1940s is not possible since the Black and Marmara seas, influencing water quality of the Golden Horn, are also suffering from anthropogenic impacts and are far less diverse than their rich diversity in 1940s. However, the Golden Horn is a good example that even the most polluted ecosystems can recover when appropriate measures are taken.

Bacterial contamination associated with estuarine shoreline development

To examine the relationships among increasing estuarine shellfish closings due to bacterial contamination, adjacent shoreline land uses and environmental variables. A 1 year study of faecal coliform bacterial contamination of a small estuary in central NC, USA was done relative to adjacent land uses. The area has experienced rapid growth in residential shoreline development including the installation of adjacent, separate docking facilities for larger boats, each <11 slips (pseudomarina) that appear to be a single marina (individual facilities of >10 slips). Six near-shore sites were selected [old developed shore (OD), undeveloped shore (UD), two pseudomarinas (P1, P2), newly developed shore (ND) and a real marina (RM)]. Five locations were spaced along the shore near each site. Paired Thursday/Monday samples were collected biweekly (summer) and monthly (other seasons). Results indicate that OD had the highest bacteria counts followed by ND, RM and P1 & P2. Three sites (OD, ND and RM) failed to meet NC shellfishing waters standards at all locations. At the pseudomarina sites 4 of 10 locations failed to meet shellfish standards while two locations at UD failed to meet these standards. There were no significant differences between paired Thursday/Monday samples. At three sites (OD, UD and P2) bacteria counts were positively correlated with increased water level due to wind tides. Any type of estuarine shoreline development may result in closing of adjacent shellfishing waters. ND had bacterial counts second only to OD in spite of the retention of vegetated shoreline buffers and very new septic systems. As expected, the RM also failed to meet shellfish standards. Unexpectedly, only four of the 10 pseudomarina locations failed to meet the standards. Weekend boat use had no effect on bacterial counts. Surface runoff from rain and shoreline flooding from increased water levels increased bacterial counts, probably as a result of suspension of surface deposited faeces from wildlife and domestic animals. Multiple docking facilities do not necessarily result in violations of shellfish water quality standards. However, the elevated bacterial counts observed along the newly developed shore suggest caution in approving the practice of allowing individual 'oyster gardening' off private piers if the oysters are intended for human consumption. The practice of automatic closure of shellfish waters around RMs was supported. Correlations of bacterial counts with time following significant rainfall suggests a sampling strategy to separate local sources of bacteria from more remote sources thus focusing limited remedial resources more effectively.

Benthic Nutrient Flux in a Small Estuary in Northwestern Florida (USA)

Benthic nutrient fluxes of ammonium (NH4+), nitrite/nitrate (NO2- + NO3-), phosphate (PO4-3), and dissolved silica (DSi) were measured in Escambia Bay, an estuary within the larger Pensacola Bay system of northwestern Florida (USA). Our study occurred during a severe drought which reduced riverine inputs to Escambia Bay. Laboratory incubations of field-collected cores were conducted on 8 dates between June and October 2000 to estimate nutrient flux, and cores were collected from locations exhibiting a range of sediment organic matter content. NH4+ flux ranged from – 48.1 to 110.4 μmol m-2 h-1, but the mean flux was 14.6 μmol m-2 h-1. Dissolved silica (DSi) fluxes were also variable (-109. 3 to 145.3 μmol m-2 h-1), but the mean net flux (9.3 μmol m-2 h-1) was from the sediment to the water column. Bay sediment fluxes for NO2-+ NO3- and PO4-3 were less variable during this period (– 7.93 to 28.73 and – 1.74 to 3.29 μmol m-2 h-1 for NO2-+ NO3- and PO4-3, respectively). Low NH4+ fluxes were similar to published estimates from lagoonal Gulf of Mexico (GOM) estuaries, possibly due to the reduced freshwater input. Diminished regeneration of phosphate relative to inorganic nitrogen observed during the study period was consistent with previous research in Pensacola Bay suggesting phytoplankton phosphorus limitation. Finally, the estimated residence time of Escambia Bay and the mean turnover times for NH4+ and NO2-+ NO3- suggested that benthic flux significantly influenced nitrogen concentrations in overlying water.

Spit development in the Mdloti River estuary, KwaZulu-Natal

Research Article| September 01, 2005 Spit development in the Mdloti River estuary, KwaZulu-Natal S.E. Garden; S.E. Garden School of Life and Environmental Sciences, Memorial Tower Building, University of KwaZulu-Natal, Durban, 4041, e-mail: 200273455@ukzn.ac.za; garland@ukzn.ac.za Search for other works by this author on: GSW Google Scholar G.G. Garland G.G. Garland School of Life and Environmental Sciences, Memorial Tower Building, University of KwaZulu-Natal, Durban, 4041, e-mail: 200273455@ukzn.ac.za; garland@ukzn.ac.za Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2005) 108 (2): 257–270. https://doi.org/10.2113/108.2.257 Article history first online: 07 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation S.E. Garden, G.G. Garland; Spit development in the Mdloti River estuary, KwaZulu-Natal. South African Journal of Geology 2005;; 108 (2): 257–270. doi: https://doi.org/10.2113/108.2.257 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract Although the importance of estuaries as ecological, geomorphological and sedimentological systems is well recognised and a number of estuarine classification schemes are referred to in literature, geomorphological behaviour of small estuaries such as those on the KwaZulu-Natal coast are not well understood. In particular the development and role of spits and bars in the functioning of small, perched estuaries needs clarification. The purpose of this study was to determine the mechanism of spit initiation and growth in the Mdloti estuary, a small perched estuary some 25km north of Durban, on the KwaZulu-Natal coast, with a view to developing an hypothesis which explains the procedure of split development and its role in the geomorphological life of the estuary. Seven generations of air photos from 1953 to 2000 were analysed, and sediment samples from four trenches and two cores located on the spit allowed recent sedimentological history to be interpreted and integrated with geomorphological development of the mouth over the last 50 years. Results showed that infrastructural developments in the upper estuary and artificial breaching of the of the mouth all had significance in determining estuarine behaviour, but that spit initiation and development after breaching was largely dependent on long-shore sediment transport. The results allowed the proposition of a sequential model for spit development for the Mdloti estuary subsequent to breaching during a flood. An offshore delta is formed by the flood and later joined by a spit bar built up by longshore drift. Ebb delta deposits are re-worked by longshore currents. As the new bar becomes emergent aeolian activity commences and the spit is gradually widened by overwash deposits, and growth continues until the estuary is completely closed off. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Competition for feeding in waders: a case study in an estuary of south temperate Europe (Mondego, Portugal)

The loss of feeding areas may pose a threat to many wintering waders because increased competition arising from reduced foraging space may force birds either to emigrate or to die. This has been demonstrated to occur in northwest European estuaries, but virtually no studies have been performed in the estuaries of southern Europe, where the loss of supratidal habitats (salines and saltmarshes), rather than intertidal habitats, are currently the main threat to waders’ habitats. If these habitats are lost, waders may be forced to move to the intertidal mudflats, perhaps increasing competition between individuals and ultimately leading to starvation or emigration. We tested this hypothesis in the Mondego estuary, a small estuary on Portugal’s west coast, which is presently under heavy human pressure. We used indirect methods to test for the occurrence of both components of intra-specific competition: interference and prey depletion. We found no evidence that either interference or depletion competition was occurring at present, either on the mudflats or in the salines. Overall, the results suggest that the intertidal mudflats may still be able to accommodate birds displaced from the destroyed supratidal salines, but modelling is required to predict the effect that the combined loss of feeding area and foraging time that this would entail would have on their fitness, and thus numbers.

Correlation between foraminifera and sedimentary environments in recent estuaries of Southwestern Spain: Applications to holocene reconstructions

A multivariate analysis of the foraminifera collected in three estuaries of southwestern Spain (Guadiana, Piedras, Tinto-Odiel) permits recognition of three main assemblages, with spatial distribution depending on sedimentary environments, grain size classes and salinity variations. Assemblage 1 ( Trochammina inflata, Jadammina macrescens) is typical of salt marsh deposits with high salinity variations and percentages of important silt. Assemblage 2 ( Ammonia beccarii, Ammonia tepida, Astrononion stelligerum, Elphidium williamsoni) includes the most abundant estuarine species, with increasing densities from the channel margin to the subtidal channel. Assemblage 3 ( Quinqueloculina seminulum, Elphidium crispum) is mainly found in the sandy sediments of the subtidal channels located near the mouth, with normal marine conditions. These results and the sedimentological interpretation of seven drill cores collected in the Domingo Rubio Channel (Tinto River) allow reconstruction of the palaeogeographic changes of this small estuary in the last ca. 6500 14C years BP. Seven phases were distinguished, with an evolution from an open marine bay to a very restricted channel limited by broad salt marshes.

Anthropogenic impacts recorded in the sediments of Lunawa, a small tropical estuary, Sri Lanka

The Lunawa Estuary has been selected as a model for studying the long-term diagnoss of tropical estuarine pollution and its impact on ecosystems. Surface and short-core sediments from the Lunawa Estuary were collected, and analyzed for total organic carbon (TOC), nitrogen, sulfur and hydrocarbon contents, hydrogen index and other related sediment properties. Water quality and surface sediment data indicate that the Lunawa Estuary is presently an anoxic water body. The upper part of the sediment cores, characterized by very high TOC values of more than 10%, and absence of bioturbation along with strong laminations indicate anoxic water since 1970 AD, determined by 14 C dating. However, before 1970 AD, lower TOC content and presence of bioturbation and homogenous sediments with animal traces suggest the presence of oxic bottom water and thus a much better physicochemical condition. The lower part of the cores may also suggest the influence of gradual global warming. Regular laminations in the upper portions of the cores probably resulted from monsoon pulses with material preserved under anoxic condition.

Spatial and temporal variability of seagrass fishes in intermittently closed and open coastal lakes in southeastern Australia

A large-scale survey of seagrass fish communities was carried out quarterly over a three-year period in six coastal lakes with entrances that were intermittently closed and open to the ocean. These coastal lakes, located along ∼400 km of the southeastern Australian coastline, ranged from 4.2 km 2 to 38.9 km 2 in water area, but experienced a similar range of salinities, temperatures, pH and turbidities over the study period. A total of 203 936 individual fish, belonging to 46 families and 93 species, were caught and released, with the most diverse families being the Gobiidae (12 species), Monacanthidae (9 species) and Syngnathidae (7 species). There were major changes in numbers of fish caught between years, accompanied by changes in the compositions of the species assemblages. These changes were associated with heavy rainfall and flooding in the region during the second year of the study, which caused the opening of all lakes to the sea, and allowed recruitment of marine spawning species. This inter-annual variability was much larger than any of the seasonal or spatial differences observed, which were inconsistent within and between the studied lakes. The salinity regime of individual lakes played a role in structuring the fish assemblages on a regional scale, rather than any obvious biogeographic factors. Artificially opening the entrance of one lake, to alleviate flooding, resulted in the loss of a large seagrass bed and a subsequent decline in recruitment of economically important fish species to that area. The research suggests that, for these small estuaries, conservation of fish diversity might best be achieved on a “whole-of-estuary” basis, rather than by zoning of areas within individual lakes. It also indicated that artificially opening the lakes, or carrying out other entrance works, should be done with great caution as the impact that these activities may have on their fish communities remains largely unpredictable.

Human settlement and coastal change in Gaza since the Bronze Age

Gaza has been characterized by important coastal changes since the Bronze Age. Around 6000 years ago, the coast comprised small estuaries at the outlets of the main wadis. During the Bronze Age, this indented coast spawned important maritime settlements such as Tell es-Sakan and Tell al-’Ajjul at the outlet of Wadi Ghazzeh, which probably served as a natural harbour. During the same period, the rate of sea level rise slowed, leading to the formation of the Nile delta and small local deltas along the coasts of the Sinai and Palestine. From the first millennium BC, the coast was regularised by infilling of the estuaries and settlements. The harbour sites became landlocked. In response, new cities, such as Anthedon, were founded on a Quaternary ridge along the present coastline. Our research project is to test and date this «model of sedimentological evolution» –abandonment of estuarine sites and re-settlement on the coastal ridge– and to compare the fluvial and coastal environmental histories to the long-term dynamics of human settlement.

A new water column profiler for shallow aquatic systems

Coupled physical and biogeochemical processes in shallow (<2 m deep) productive systems must be observed on fine temporal and spatial scales with automated sampling and monitoring devices. We developed a pump profiler system that can sample six to eight depths at 10-cm resolution every 30 min. The system is economical, secure from vandalism, portable, and capable of integration with a real-time remote monitoring system. Solenoid valves select the suction depth, and a diaphragm pump delivers water to a flow cell where temperature, oxygen, pH, specific conductivity, turbidity, oxidation reduction potential, and fluorescence are measured with probes mounted on a water quality sonde. A microcontroller is used to direct the operation of the system. Water column disturbance and maintenance requirements are minimized by eliminating exposed moving parts. The data can be retrieved remotely and graphically displayed on the Internet in real time. The system has been deployed successfully in two freshwater ponds and a tidal saltwater system. The pump profiler is used to study coupled physical biogeochemical processes in shallow systems with strong diel cycles and large density and chemical gradients. Applications may include studies in aquaculture ponds, storm water retention ponds, shallow lakes, and small estuaries.

Temporal variability in nitrification rates and related biogeochemical factors in Monterey Bay, California, USA

The scales of temporal variability in the rate of ammonium oxidation and a suite of related biogeochemical parameters were investigated in the surface layer of the water column of Monterey Bay, California, on the west coast of the USA. Samples were collected on bimonthly (approx. every 2 mo) cruises during the course of 2 yr. The signal of El Nino was evident in the water column temperature and nitrate distributions during the initial cruise in February 1998. Throughout the 2 yr period, variation in temperature and salinity was small and consistent with seasonal upwelling. The biological parameters, however, varied much more than might have been predicted by the minimal variability in hydrographic signals. Ammonium assimilation rates, chlorophyll a con- centrations and bacterial abundance varied by 41-, 65- and 147-fold, respectively. Ammonium oxida- tion rates often exhibited a subsurface maximum near the bottom of the euphotic zone, and varied by a factor of 4.5 over the 2 yr study. The presence of the rate maximum was not obviously related to the dominant seasonal signals of hydrography or to other biological variables. Nitrification rates were much less variable in the bay than in Elkhorn Slough, a small estuary that opens onto the bay. The small variability in ammonium oxidation rates may be related to more dynamic responses in the com- munity composition of the ammonia-oxidizing bacteria. Different groups of ammonia-oxidizing bac- teria were detected as dominants in clone libraries from the Monterey Bay and Elkhorn Slough. The time scale of bimonthly sampling was evidently inadequate to resolve the response of nitrification rates to direct physical forcing in the bay.