Bottom Of Bay Research Articles

Flow and geochemistry of groundwater beneath a back-barrier lagoon: The subterranean estuary at Chincoteague Bay, Maryland, USA

To better understand large-scale interactions between fresh and saline groundwater beneath an Atlantic coastal estuary, an offshore drilling and sampling study was performed in a large barrier-bounded lagoon, Chincoteague Bay, Maryland, USA. Groundwater that was significantly fresher than overlying bay water was found in shallow plumes up to 8 m thick extending more than 1700 m offshore. Groundwater saltier than bay surface water was found locally beneath the lagoon and the barrier island, indicating recharge by saline water concentrated by evaporation prior to infiltration. Steep salinity and nutrient gradients occur within a few meters of the sediment surface in most locations studied, with buried peats and estuarine muds acting as confining units. Groundwater ages were generally more than 50 years in both fresh and brackish waters as deep as 23 m below the bay bottom. Water chemistry and isotopic data indicate that freshened plumes beneath the estuary are mixtures of water originally recharged on land and varying amounts of estuarine surface water that circulated through the bay floor, possibly at some distance from the sampling location. Ammonium is the dominant fixed nitrogen species in saline groundwater beneath the estuary at the locations sampled. Isotopic and dissolved-gas data from one location indicate that denitrification within the subsurface flow system removed terrestrial nitrate from fresh groundwater prior to discharge along the western side of the estuary. Similar situations, with one or more shallow semi-confined flow systems where groundwater geochemistry is strongly influenced by circulation of surface estuary water through organic-rich sediments, may be common on the Atlantic margin and elsewhere.

In situ microscale variation in distribution and consumption of 2 : A case study from a deep ocean margin sediment (Sagami Bay, Japan)

A transecting microprofiler documented a pronounced small-scale variation in the benthic O2 concentration at 1450-m water depth (Sagami Bay, Japan). Data obtained during a single deployment revealed that within a sediment area of 190 cm2 the O2 penetration depth varied from 2.6 mm to 17.8 mm (average; 6.6 ± 2.5 mm) and the diffusive O2 uptake, calculated from the vertical concentration gradient within the diffusive boundary layer, ranged from 0.6 mmol m−2 d−1 to 3.9 mmol m−2 d−1 (average; 1.8 ± 0.7 mmol m−2 d−1, n = 129). However, correction for microtopography and horizontal diffusion increased the average diffusive O2 uptake by a factor of 1.26 ± 0.06. Detailed 2D calculations on the volume-specific O2 consumption exhibited high variability. The oxic zone was characterized by a mosaic of sediment parcels with markedly different activity levels. Millimeter- to centimeter-sized ‚‚hot spots’’ with O2 consumption rates up to 10 pmol cm−3 s−1 were separated by parcels of low or insignificant O2 consumption. The variation in aerobic activity must reflect an inhomogeneous distribution of electron donors and suggests that the turnover of material within the oxic zone to a large extent was confined to hot spots. The in situ benthic O2 uptakes, measured during four cruises, reflected a seasonal signal overlying the observed small-scale variability. The annual benthic mineralization balanced ~50% of the estimated pelagic production. However, the central bay is characterized by a significant downslope sediment transport, and mass balance estimates indicate 90% retention of the total organic material reaching the bottom of the central bay.

Characterization of sedimentary deposits at the confluence of two tributaries of the Pará River estuary (Guajará Bay, Amazon)

Guajará Bay, located at the right margin of the Pará River estuary (Amazon) is formed in the confluence of Guamá and Acará–Moju rivers. It has low-depth zones (∼5 m) and deep channels (∼25 m). The ebb channel is located in the west section, where there is intense erosion of the margin. The flood channels and intertidal mudflats, which stretch out from north to south along the shore of the city of Belém do Pará, are in the east section. There are sandy (northwest) and muddy sedimentary deposits (east–southeast). Some 70% of Guajará Bay's bottom is covered by mud. The depositation of such muddy sediments and the formation of a point bar in the south section (Guamá River mouth) happen due to a decrease in the intensity of tidal currents to the south and of fluvial currents to the north. However, the hydrodynamic regime is high, which is proved by the low clay amounts. The sand deposits in the northwest section indicate strong tidal currents. The vast area of the bottom that is covered by mud (∼90 km 2) and the intertidal mudflats (∼150 m wide) in Guajará Bay hint the extent of the contribution and sediments flow from Guamá and Acará–Moju rivers (drainage basin total area of ∼87,400 km 2) to the Pará River estuary. The regular rainfall regime, typical of the Amazon region, keeps the considerable discharges of such rivers and their high turbidity (Secchi depth ⩽0.5 m) in the investigation area. Generally speaking, the low topography, the great fluvial subsidy and the action of tidal currents are the main controlling elements of the depositation and dispersion of sediments in Guajará Bay.

Speciation of mercury in water at the bottom of Minamata Bay, Japan

Total mercury (T-Hg) and methylmercury (MeHg) concentrations were determined in water at the bottom, in the suspended solid, and in the surface sediment of Minamata Bay to assess the remobilization of mercury from the sediment into the water column. The water and sediment samples were taken from the bottom of the bay using a gravity core sampler at nine locations in October 2002 and six locations in April 2005. The average concentration of T-Hg and the proportion of MeHg in the sediment were 3.71 ± 1.90 mg/kg and 0.27 ± 0.28%, respectively. The water contained 1.80 ± 1.00 ng L − 1 of T-Hg, which was higher than the value reported for the upper-middle depth of Minamata Bay. The results suggest that the sediment is an important source of mercury in the water of Minamata Bay. The percentage of MeHg in the water at the bottom was 50.7 ± 24.6%, also considerably higher than in the upper-middle layer of the water column, suggesting that MeHg may be the predominant form of mercury released from the sediment into the water. The percentage of MeHg was lower in the resuspended sediment than in the surface sediment. The amount of mercury eluted from the sediment into the water was estimated at 0.46 kg and 0.11 kg per year for T-Hg and MeHg, respectively.

생태계 모델을 이용한 진해만의 COD의 거동과 분포특성 평가

To find proper water quality management strategy for oxygen consumption organic matters in Jinhae bay, the physical process and net supply/decomposition in terms of COD was estimated by three-dimensional eco-hydrodynamic modeling. The estimation results of physical process in terms of COD showed that transportation of COD was dominant in loading area from land to sea, while accumulation of COD was dominant in <TEX>$middle{\sim}bottom$</TEX> level. In case of surface level, the net supply rate of COD was <TEX>$0{\sim}60\;mg/m^2/day$</TEX>. The net decomposition rate of COD was <TEX>$0{\sim}-0.05\;mg/m^2/day$</TEX>(<TEX>$-5{\sim}-10$</TEX> m, in depth) to 2 level, and <TEX>$-0.05{\sim}-0.20\;mg/m^2/day(10m{\sim})$</TEX> to bottom level. These results indicate that the biological decomposition and physical accumulation of COD are occurred for the most part of Jinhae Bay bottom. The variation of net supply or net decomposition rate of COD as reducing land based input loading is also remarkable. Therefore, it is important to consider both allochthonous and autochthonous oxygen demanding organic matters to improve the water quality of Jinhae Bay.

High resolution acoustic characterization and change detection to evaluate hurricane effects on a coastal bay bottom

Using high-resolution acoustics (sidescan sonar, chirp sonar subbottom, and echo sounder profile data) the shallow surface and subsurface of Sister Lake (Terrebonne Basin) of coastal Louisiana’s deltaic plain was imaged pre- and post-hurricanes Katrina and Rita. The pre-hurricanes survey in May 2005 imaged the entire lake bottom. To assess the effects of hurricanes Katrina and Rita, a second survey in October 2005 included acoustic resurveying of corridors of data covering all major sectors of the lake. Regions of sidescan reflectance differences between pre- and post-storm periods, corroborated with regions of onlapping sediment or zones of scour in the chirp sonar subbottom data, show areas both of sedimentation and erosion between surveys. Ground truth box cores were collected to calibrate acoustic data. Preliminary image processing results of the georeferenced pre- and post-storms sidescan datasets indicate 60% of the area experienced sedimentation and 40% was scoured between surveys. Amplitude reflectivity of chirp horizons were mapped, and incorporated with sidescan amplitude and texture attributes in change detection analysis. Standardized digital processing, supervised classification, and change detection techniques are developed to characterize the bay bottom and shallow subsurface and to assess and quantify storm effects. [Work supported by NOAA NA03NMF4520316.]

Susceptibility of a northern Gulf of Mexico estuary to hypoxia: An analysis using box models

The extent of hypoxia and the physical factors affecting development and maintenance of hypoxia were examined for Pensacola Bay, Florida (USA) by conducting monthly water quality surveys for 3 years (2002–2004) and by constructing salt-and-water balance box models using the resulting data. We also analyzed data from earlier summer probabilistic water quality surveys (1996–1999). Hypoxia (O 2 < 2.0 mg L −1) affected an average of 24% (range = 16–36%) of the Bay bottom during 1996–1999 summer surveys; similar results were obtained using the 2002–2004 monthly survey data. The water column in Pensacola Bay was usually well-stratified, apparently as a result of the low amplitude (<50 cm) diurnal tide, which provides low mixing energy. Vertical diffusivity at the pycnocline was between 0.002 and 0.02 cm 2 s −1, 10-fold less than comparable estimates for Chesapeake Bay, Maryland/Virginia. Residual (sub-tidal) estuarine circulation was sluggish, with landward velocity in the bottom layer between 1 and 4 cm s −1 during summer. The observed physical transport regime severely limits exchange of bottom waters and is very conducive to development of hypoxia. Net non-conservative O 2 fluxes and physical O 2 inputs were generally in a dynamic balance during summer, such that the median imbalance, the accumulation or depletion of O 2, was only 11% of the non-conservative flux. Computed net non-conservative O 2 fluxes for the lower water column and sediments were generally low relative to other estuaries (<0.5 g O 2 m −2 d −1), indicating an absence of eutrophic conditions. This suggests that the current extent of hypoxia in Pensacola Bay may be largely attributable to natural susceptibility to hypoxia resulting from physical factors. Balanced O 2 metabolism or net autotrophy below the pycnocline was observed for some segments of the Bay. We hypothesize that O 2 production resulting from photosynthesis below the pycnocline sometimes offset O 2 consumption in Pensacola Bay bottom waters, potentially reducing development of hypoxia.

OS8-2-6 Behavior of sediment lifted up by swirling bubbling jet in bottomless container

Mixing of liquid in a container by gas injection is widely used in many industrial fields. For example, it has been utilized in steelmaking processes, chemical engineering processes and remediation of polluted sediments. We focus on the treatment of contaminated sediments on the bottom of bays and lakes using a swirl motion of a bubbling jet and ozone. In this study, we mention about the behavior of sediment lifted up by swirling bubbling jet generated with a J-shaped lance in a bottomless container. Investigation is carried out on the occurrence condition and basic characteristics of the swirling bubbling jet. The occurrence region is affected by the lifted sediments. The measured values of the basic characteristics can be approximated by empirical equations proposed previously for a bottom blown container without sediments. The period of the swirl motion can be satisfactorily approximated by the period of the rotary sloshing.

Contamination of Sediments and Proposed Containment Technique in a Wood Pool in Shimizu, Japan

Abstract The objective of this study is to evaluate the contamination of sediments, in order to determine a remediation method for a local bay bottom. To achieve this, 12 surface-sediment samples were obtained from a wood pool located in the inner part of Shimizu Port, Japan, and were subjected to physical and chemical analyses. The results show that the concentrations of the heavy metals measured were relatively high. The concentrations of copper and zinc in the sediment samples were higher than the probable effect levels of marine sediments provided by the Canadian Sediment Quality Guidelines. The high concentrations obtained are probably due to the high organic content resulting from humus. The separation of organic matter might be useful as a remediation technique for dredged materials. A containment technique for dredged sediments using permeable bags is therefore proposed.

HABITAT PREFERENCES OF SURFACE-DIVING WATERBIRDS AND AMERICAN WHITE PELICANS WINTERING IN REDFISH BAY, TEXAS

Habitat preferences were determined for a guild of surface-diving waterbirds wintering in Redfish Bay, Texas: common loon (Gavia immer), eared grebe (Podiceps nigricollis), pied-billed grebe (Podilymbus podiceps), double-crested cormorant (Phalacrocorax auritus), red-breasted merganser (Mergus serrator), and American coot (Fulica americana). American white pelican (Pelecanus erythrorhynchos) also was included because it occupies habitats similar to those of the surface divers. Between November 2001 and April 2002, the locations of 4,232 surface divers and American white pelicans using aquatic habitats in Redfish Bay were recorded and entered into a GIS that included a National Wetlands Inventory layer. Bird habitat preferences-avoidances were determined using a test based on Bonferroni's inequality. American coots, American white pelicans, and pied-billed grebes preferred shallower estuarine subtidal seagrass beds, whereas common loons, double-crested cormorants, and eared grebes preferred deeper estuarine subtidal unconsolidated bay bottom. Red-breasted mergansers showed no habitat preferences.

Ground Water Beneath Coastal Bays of the Delmarva Peninsula: Ages and Nutrients

AbstractTo complement a large‐scale geophysical investigation of occurrence and discharge of fresh water beneath Delaware, Maryland, and Virginia (Delmarva) coastal bays, we measured (1) salinity and nutrient concentrations in ground water samples from several offshore coring sites and (2) a suite of chemical and isotopic parameters, including age tracers, in ground water samples from a Delaware site. Samples were collected in a variety of Holocene and Plio‐Pleistocene sediments in nearshore and offshore areas of the bays. Ground waters that were significantly fresher than overlying waters were found in plumes up to at least 15 m thick extending to more than 500 m offshore in some areas. Steep salinity and nutrient gradients occur within a few meters of the sediment surface in most locations studied. The zone of transition from deeper fresher waters to shallower brackish waters is generally thin near shore, but thickens and becomes more gradual offshore. Ground water ages at the Delaware site were mostly &lt; 50 yr in both fresh waters and brackish waters up to 22 m below the bay bottom. Water chemistry and age data indicate that fresh water plumes beneath the estuary are active extensions of the surficial aquifer carrying nitrate from recharge areas on land, whereas brackish ground water surrounding the fresh water plumes is recharged beneath the estuary and contains ammonium and phosphate released by diagenesis of shallow estuarine sediments. Denitrification affects some of the fresh water nitrate before it mixes with brackish ground water or discharges to surface water.

Controls on Surficial Materials Distribution in a Rock-Framed, Glaciated, Tidally Dominated Estuary: Cobscook Bay, Maine

Surficial materials were mapped on the bottom of Cobscook Bay, ME, through aerial photography of intertidal habitats, side-scan sonar, and seismic reflection profiling of subtidal regions. Like many other estuaries in northern New England, this rocky, macrotidal estuary has only slight riverine input and contains an abundance of till and fine-grained glacial-marine sediment. Contrary to conceptual models of estuarine sediment and habitat distribution, grain size does not become finer and habitats lower in energy in a landward direction within the estuary. The irregular shoreline shape, imparted by bedrock, forms a series of narrow constrictions separating broad bays. More than 70% of the bottom of the estuary is floored by gravel and rock; mud deposits are located in shallow-water coves throughout the Bay and in two large deposits in the Central Bay. Here, circulation models predict two large gyres form because water cannot pass through a bedrock constriction quickly enough. Natural gas is present in sufficient quantities in the sediment column to facilitate sediment mass movements near the mud deposits. Almost 60% of the intertidal zone is composed of mudflats that are uniformly distributed within and along the outside margin of the Bay, with increasing abundance of bedrock in a landward direction. Small beaches occur wherever coarse-grained glacial sediment erodes from bluffs. These observations depart from existing conceptual models of estuarine sediment distribution based on coastal plain estuaries and suggest that better understanding of biotic habitat or contaminant distribution in rocky glaciated estuaries will require more localized models. These estuaries appear more complex than coastal plain estuaries because of the unique outcrop pattern of bedrock and glacial deposits in each bay.

A Preliminary Survey of the Subtidal Macrobenthic Invertebrates of Cobscook Bay, Maine

Cobscook Bay, a boreal, macrotidal estuary in the northeastern Gulf of Maine is noted for its species richness and has been the site of extensive natural history investigations. In spite of this level of investigative activity, no quantitative survey of the subtidal, macroinvertebrate communities exist. Here we present the results of a 1975 benthic grab survey of outer Cobscook Bay prior to recent salmon aquaculture and port development. The limited 11-station survey resulted in the identification of 172 taxa. Densities ranged from 870 to 12,970 m−2. Multivariate and qualitative analyses clearly dissected the station set into sandy cove stations and coarse sediment channel stations. Cove stations were characterized by burrowing and tube-dwelling infauna, while channel station fauna was epifaunal. Community distribution is controlled by strong tidal currents and resulting sharp geological discontinuities. Because 70% of the Bay bottom is floored by gravel, the epifaunal community characterizing the channel stations may be the most representative of the Bay. The grab sampler certainly underestimated large filter feeders that may be important in the nutrient budget of the Bay. Future surveys need to be more extensive and use a combination of sampling methods to quantitatively measure all components of the community.

Spatial variability of the biogeochemical composition of surface sediments in an insular coral reef ecosystem: Moorea, French Polynesia

The spatial variability of the biogeochemical composition of surface sediments was investigated around Moorea, French Polynesia. This study complements other ones conducted in Moorea to assess coral reef “health”. A total of 35 stations were sampled at four sites around the island, on the following geomorphological units: fringing reef of the bays, fringing reef of the lagoon, channel, barrier reef, pass, sandy slope, bay bottom. We found strong spatial heterogeneity in the biogeochemical composition of surface sediments. The multivariate analyses (PCA and clustering) distinguished four major sediment types around Moorea, and a gradient between the bayheads and the bay entrances. The first type corresponds to the inner half bay bottoms, and clearly represents the “terrigeneous” influence. This terrigeneous sediment type was mainly characterised by a clear deficit in carbonates and, conversely, by an enrichment in organic compounds (organic carbon (OC), nitrogen (N), as well as total amino acids (AA) and carbohydrates (CH) in mg g −1) that were highly degraded. Two other sediment types were influenced by the carbonated reef system. They were highly carbonated (inorganic carbon (IC) around 11%; i.e., carbonates around 90%), and showed low organic compound concentrations. They were also characterised by high hydrolysable organic carbon (HOC) concentrations. These two “reef-characteristic” sediment types can be distinguished by their N concentrations and C/N ratio. The fourth type represents a transition between “reef-characteristic” and “terrigeneous” sediment types. Our results showed that HOC, total AA and CH, examined for the first time in coral reef ecosystems, were reliable descriptors for spatial variability surveys, together with the more ‘classical’ descriptors: IC, OC and N.

Distinctive sedimentary processes in Guanabara Bay - SE/Brazil, based on the analysis of echo-character (7.0 kHz)

Guanabara Bay bottom sediments and seabed characteristics were analysed using high-resolution (7 kHz) sub-bottom profiles associated with particle size analyses of 92 bottom sediment samples. Eight types of echo-characters were identified revealing the strong relation with the particle size distribution. Sandy bottom areas presented strong echo reflections, without sub-bottom penetration (Echo types I and III), while in muddy areas sub-bottom reflections showed the acoustic basement delineating buried sugar-loaf hills and infilled-valley features (Echo type IV). The presence of shallow gas within the sediments is indicated by acoustic blanket and a series of bottom-multiple reflections (Echo types Va and Vb). Erosion by bottom currents and artificial mechanical dredging are suggested by truncations of sub-bottom reflections and a wrinkled seabed surface (Echo types VI and VII). Crystalline basement outcrops on the seabed are recognized by multiple or single hyperbolae with varying elevations above the bay bottom (Echo type II).

日本の海産移入生物―沿岸生態系への新たなる脅威 東京湾における移入種イッカククモガニとチチュウカイミドリガニの生活史と有機汚濁による季節的貧酸素環境での適応性

Two introduced crab species, Pyromaia tuberculata and Carcinus aestuarii, occur abundantly in organically polluted waters in Japan. Population studies of these crabs have been conducted in Tokyo Bay, in which summer hypoxia causes destruction of the benthic animal populations on the bottom of the innerhalf of the bay. In fall, a population of P. tuberculata quickly recolonizes that bottom, which has recovered from the hypoxia, by settlement of larvae. Settled crabs reach maturity by the next spring, then release larvae until the subsequent summer hypoxia. Released larvae disperse to the outerhalf of the bay, resulting in recruitment of juveniles into the local population. These recruits reach maturity before the fall under the normoxic conditions prevailing there, then release larvae for recolonization of the innerhalf of the bay. Carcinus aestuarii grows along the shores of river-mouths and in a lagoon of the inner bay, but migrates out onto the bay bottom during fall to spring, when it releases larvae. Released larvae settle along the shores during the spring. Settled crabs grow on the shores with adult crabs that had returned from the bay bottom. Thus the crabs on the shores avoid encountering the bottom hypoxia. These results suggest that the main factor that has allowed the establishment of the new introduced populations in Tokyo Bay is complementarity between the life cycle of these crabs, including adult migration or larval dispersal, and the seasonal availability of a habitat that is recovering from hypoxia.

HEXAGONOIDAL PARTITIONING AND QUASI-SINGLE BONDS IN BENZENOID HYDROCARBONS

The concept of fully benzenoid hydrocarbons (molecular graphs; FBHs) is generalized. Each full-hexagon unit (aromatic sextet) in a FBH is replaced with a larger “hexagon-shaped” unit (subgraph; e.g., naphthalene, pyrene, coronene, or ovalene units). Such a molecular species may be called a “fully hexagonoid” hydrocarbon (FHHs). The Pauling bond order calculation suggests that a bond (edge) which interlinks one hexagon-shaped unit with another in the bottom of bays of FHH is quasi-single, if the two units are connected by more than two bonds. As a consequence, the hexagon-shaped units are delocalized locally in the hexagonoidal (graph-theoretical) partitioning.

Chemical Composition and the Origin of Suspension Particles in Liang-Dong Bay (Yin-Yang Sea), Northern Taiwan

A phenomenon of mixing blue and brown seawater, called Yin-Yang Sea, has existed for decades in Liang-Dong Bay. In order to determine the chemical composition and origin of pollutants in the bay, each of 5 water samplesfrom the stream and bay were collected for chemical analyses. Meanwhile, suspension particles in the bay, the sediments on the bottom of bay and the precipitation on the bottom of the stream were also collected for chemical, X-ray diffraction and particle size analyses. The suspension particles are amorphous and are predominantly composed of Fe(OH) 3 . this is showen by the solubility products of water samples in the bay being higher than the k s p of Fe(OH) 3 . The deposits on the bottom ofthe stream also show similar results. However, the chemical concentrations of major ions, e.g. Na + , K + , Ca + 2 , Mg + 2 , Cl - and SO 4 -2, are much higher in the bay water than of the stream water. Nevertheless, Fe + 2 , Mn + 2 , Cu + 2 and Si + 4 show positive anomalies in the lower stream where the abandoned pits are located. Thus, it is assumed that minerals in the pits, such as pyrite and marcasite, are the main source supplying iron through weathering. Iron released by minerals is carried by the stream and arrives in the bay in hours. Since the oxidation rate becomes very slow in the bay because of the effects of salts and neutral pH values, most of the particles of Fe(OH) 3 form in the bay gradually.

Internal recycling of particle reactive organic chemicals in the Chesapeake Bay water column

Hydrophobic organic contaminants (HOCs) may be used as tracers of particle dynamics in aquatic systems. Internal cycling of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were studied in the mesohaline Chesapeake Bay to assess the role of resuspension in maintaining particle and contaminant inventories in the water column, and to compare settling and suspended particle characteristics. Direct measurements of sediment resuspension and settling conducted in conjunction with one of the sediment trap deployments indicate reasonable agreement between measurements of particle flux using the two different methods. Organic carbon and PCB concentrations in settling solids collected in near-surface sediment traps were remarkably lower than concentrations in suspended particles collected by filtration during the trap deployments, but higher PAH concentrations were found in the settling particles. The different behaviors of PAHs and PCBs in the settling particles are due to their different source types and association to different types of particles. Sediment trap collections in near bottom waters were dominated by resuspension. Resuspension fluxes of HOCs measured 2 m above the bay bottom were as high as 2.5 μg/m 2 day for total PCBs and 15 μg/m 2 day for fluoranthene, and were 25 and 10 times higher than their settling fluxes from surface waters, respectively. HOC concentrations in the near bottom traps varied much less between trap deployments than HOC concentrations in the surface traps, indicating that the chemical composition of the resuspended particles collected in the near bottom traps was more time-averaged by repeated resuspension than the surface particles.

Dissolved Oxygen Depletion in a Small Deep Lake with a Large Littoral Zone

ABSTRACT Advection and its influence on water quality (density currents and the fate of transported materials, metalimnetic oxygen depletion, etc.) are well established for reservoirs and other lakes with well-defined inflows. This paper provides an example of the potential importance of these processes in small lakes with limited inflow. Viewing such lakes as one-dimensional systems may severely limit our understanding of their dynamics. Holland Lake, a small and deep mesotrophic lake (0.14 km2 surface area and 18.8 m maximum depth) has been considered for stocking with brown trout because it provides extensive cold-water during the summer. Unfortunately, an anoxic layer of about 1.5 to 3 m thickness develops in the upper metalimnion resulting in a negative heterograde dissolved oxygen profile, and eliminating any trout habitat during July and August. The findings of a field study suggest that the occurrence of the metalimnetic oxygen minimum is related to the presence of substantial macrophyte beds in the shallow bays, the particular morphometry of the lake (69% littoral zone), and a significant groundwater inflow and outflow. Density current intrusions that transport oxygen depleted water of high detritus content from the bottom of the shallow bays into the metalimnion of the deep basin in early summer are consistent with exceptionally high observed oxygen depletion rates. It is this horizontal convective transport of materials within the lake in addition to phytoplankton settling from the photic zone above, that strongly affects the dissolved oxygen deficiency in the upper metalimnion of the deep main basin. To create a brown trout habitat, metalimnetic aeration will be required.