Variability Of Water Properties Research Articles

The spatial and temporal distribution of neodymium isotopic composition within the Rockall Trough

Rare Earth Element (REE) concentrations and Nd isotopic compositions (εNd) of five new seawater profiles scattered across the Rockall Trough (North-East Atlantic) were investigated in order: (1) to establish the seawater εNd distribution in the Rockall Trough, which is poorly known so far; (2) to identify the southward-flowing Wyville-Thompson Ridge Overflow Water (WTOW) originating from the Nordic Seas; (3) to evaluate the potential impact of lithogenic sources on the seawater εNd in the Rockall Trough. Combined with two previously published seawater stations, the results reveal a spatial εNd gradient in the upper layer (roughly the first 900 m) of the Rockall Trough with εNd values ranging from −14.9 ± 0.3 to −11.6 ± 0.2. The influence of Nd lithogenic inputs through seawater-sediment interactions have been found to be likely negligible, so the spatial gradient has been attributed to the relative influence of unradiogenic Subpolar Gyre (SPG) water carried by the North Atlantic Current (NAC) and more radiogenic water derived from the Subtropical Gyre (STG) flowing into the Shelf Edge Current (SEC) along the European margin. Freshwater from the interior seas (Northern UK) is an additional source of radiogenic εNd, although it seems restricted to the shallow continental shelf. Below the upper layer, WTOW has been characterized for the first time with εNd (mean value of −13.8 ± 0.5; n = 9) as a homogeneous intermediate water body between 600 and 1200 m. The results reveal a strong modification of the outflowing water from the Norwegian Sea that cascades through the Wyville-Thompson ridge, as WTOW in the Rockall Trough is composed of more than 80 % Atlantic water. On the western flank of the Rockall Trough, a deep WTOW component has been identified that is responsible for a modification of the Labrador Sea Water (LSW) εNd values (-13.0 ± 0.3 to −12.1 ± 0.3). Two stations separated by only a few kilometers from each other but sampled four years apart (2012 and 2016) show a multi-annual variation of water properties and εNd values (∼1 ε-unit) for the first 800 m, pointing to a change in the relative contribution of both SPG and STG to the composition of water flowing in the Rockall Trough to the Nordic Seas. Overall, these results confirm that εNd can be used to assess the water mass composition in the Rockall Trough, allowing to reconstruct North Atlantic gyre dynamics in paleoceanographic studies.

Multivariate analysis of the surface water in tropical river-estuary-sea continuums with changing land use.

The monitoring and assessment of surface water properties has been mainly conducted for freshwater rivers using multivariate analyses. The present study aimed to evaluate the effectiveness of introducing the absorption spectrum of water in order to develop a better monitoring and assessment technique for the surface waters of a river-estuary-sea continuum. Fourteen variables were measured at 17 different sites along three rivers, including estuaries and coastal sea, in Brunei Darussalam, Borneo, from August 2017 to December 2020. Among the 17 sites, freshwater streams surrounded by primary forests and coastal seawaters had the lowest ranges of the absorption coefficient at 350nm, suspended solids, and nutrients, but had the highest range of dissolved oxygen concentration. The other sites were more or less affected by natural leaching of chromophoric dissolved organic matter (CDOM) from forests, soil runoff from agricultural lands, and wastewater discharge from urban and industrial activities. The principal component analysis (PCA) showed that four principal components were significant and explained 91% of the total variance in the dataset. Four most explanatory factors were also extracted using the factor analysis (FA). In addition to the absorption spectrum, only seven basic water variables (salinity, pH, dissolved oxygen, total suspended solid, particulate organic matter, particulate inorganic matter, phosphate) were found to be necessary to assess the spatial variations in water properties at the present river-estuary-sea continuum. We conclude that it is important to include absorption spectrum data in water monitoring programs for more efficient and comprehensive assessment at land-sea interfaces.

Numerical investigation on the drag characteristics of supercritical water flow past a sphere

Numerical simulation has become a useful approach to explore the complex physical and chemical process inside the supercritical water (SCW) fluidized bed reactor. Due to the drastic and non-linear variation of water properties near pseudocritical point, the flow field and drag coefficient of SCW flow past a cold particle are considerably different from that of conventional flow. Therefore, in this work, particle-resolved numerical investigation is conducted to study the flow field and drag characteristics under the influence of the special water properties variation. Through varying the enthalpy corresponding to the particle surface temperature, which will be called the particle surface enthalpy for short, in a wide range, it realizes the study under different properties variation tendencies. The simulated results demonstrate that the variations of drag coefficient versus Reynolds number (Re) and particle surface enthalpy are in good regularity when taking the freestream temperature as reference temperature. The drag coefficient is enhanced greatly at high enthalpy difference between particle surface and inflow, and the enhancement is mainly contributed by that of the frictional drag coefficient. Moreover, the drag coefficient variations under different pressures are in good agreement when cases are set with the same inflow and particle surface enthalpies, respectively. By fitting the simulated results, a new drag coefficient correlation is developed for Re range of 10–200 with consideration of the influence of the special properties variation. The fitting quality is good that the maximum deviation between the new correlation and simulated data is 13.92%, and the mean deviation is 3.67%.

Temporal variation of power production via reverse electrodialysis using coastal North Carolina waters and its correlation to temperature and conductivity

Global estimates of electricity generation from coastal salinity gradient energy resources rely on the underlying assumption that these gradients are spatially and temporally stable. Refining these estimates requires a better understanding of coastal variations in water properties and their impact on power production. This study investigated power output in reverse electrodialysis (RED) cells by coupling seawater samples collected from three different sites along coastal North Carolina at five different sampling dates between 2016 and 2017 with wastewater effluent from a wastewater treatment facility as the dilute solution. We found that power density did not vary substantially across the sampling dates except for one notable drop in power for a sample collected during an approaching hurricane. For all sites, power output peaked during the summer season. Using our experimental results, we developed a semi-empirical predictive model of RED power output as a function of temperature and conductivity. The model was able to predict power density within approximately 20% of the experimental power densities for the seawater samples used in this study and others in the literature. Combining our modeling approach with temporal conductivity and temperature data may help identify promising sites for coastal salinity gradient energy installations.

Variability and Trends of the Alaska Gyre From Argo and Satellite Altimetry

AbstractThe interannual variability and trends of the Alaska Gyre and Gulf of Alaska (GOA) circulation are examined using meridional geostrophic transport from Argo temperature and salinity (2004–2017) and altimetric sea surface height (1993–2017). More than half of the top 1,500 m meridional transport variability in the Alaska Gyre is accounted for by a statistical mode strongly correlated with the Pacific Decadal Oscillation (PDO) index, consistent with the PDO exerting a major influence on North Pacific sea surface temperature variability. During a positive phase of the PDO, the zero‐transport streamline separating the subtropical from the Alaska Gyre is shifted to the south from its mean position, while more transport is diverted northward, associated with a stronger and larger Alaska Gyre. Additionally, over the 25‐year altimetric record there is a linear, increasing trend in strength of the Alaska Gyre (but not in areal extent), accompanied by an increasing trend for the incoming North Pacific Current. The effect of the PDO transport mode on GOA circulation is weak. Temperature and salinity volume averaged for the GOA covary with the PDO index, with warmer and fresher waters during a positive phase. Despite correlated anomalies for temperature, salinity, and northward transport into the GOA, however, geostrophic advection from the south contributes only minimally to the interannual variations of water properties in the GOA. An exception was the marine heat wave of 2013/2014 and its aftermath when temperature advection from the south played a more appreciable role for warming and subsequent cooling of the GOA.

Characterization of Various Air Plasma Discharge Modes in Contact with Water and Their Effect on the Degradation of Reactive Dyes

Plasma in- or in-contact-with liquid is an emerging technology that has high potential for use in liquid treatment applications. Due to the simultaneous production of highly reactive species, plasmas can efficiently eliminate pollutants that are difficult to remove using conventional methods. In this study, we investigate an AC-driven air plasma in contact with water, generated using five discharge modes. Modes 1, 2, and 3 are run at air-gap distance of 1, 3, and 3.5 mm, respectively, at a repetition rate of 10 kHz (sinusoidal waveform). Water polarity alternates between cathode and anode in modes 1 and 2, whereas mode 3 produces anode polarity only. Mode 4 is similar to mode 1, but with a repetition rate of 5 kHz, while mode 5 is similar to mode 3, but without the high-voltage preceding discharge when water is anode. The electrical characteristics of each discharge mode are presented in detail, and variations in water properties (namely water acidity and conductivity) are also discussed. The effect of discharge mode on the degradation rate of methylene blue (MB), a standard pollutant, is also investigated. Modes 1, 2, and 4 exhibit comparable MB degradation efficiencies, indicating insignificant dependence neither on air-gap distance or number of discharges. The difference between the efficiencies obtained using modes 3 and 5 suggests a substantial effect of the electric field applied between two successive discharges.

Anthropogenic Disturbance of Tidal Variation in the Water Properties and Phytoplankton Community of an Estuarine System

Tidal forcing is an important regulator of short-term variation in water properties and phytoplankton dynamics in estuaries. Tidal interactions with regulated freshwater discharge into estuaries that are affected by engineered structures such as sea embankments remain poorly understood. We examined tidal variations in the macrotidal (3–6 m) Yeongsan River estuary of South Korea, which receives regulated freshwater from a sea embankment. Semidiurnal variations in water properties and the phytoplankton community (size and taxonomic groups) were investigated fortnightly during four monitoring campaigns at a fixed station over daily cycles at neap and spring tides during both the dry (April–May 2012) and wet (August 2012) seasons. We calculated correlations and performed multivariate statistical analyses to identify the major factors affecting tidal variations. We found no consistent or predictable variations in water quality or the phytoplankton community over the fortnightly or semidiurnal tidal cycles. These parameters were more likely dependent on the extent of recovery from artificial freshwater discharge than on the tidal forcing, which is supported by the absence of any significant correlations between tidal height and water properties or phytoplankton features. Multivariate statistical analysis showed that tidal variation in the taxonomic community may be associated with freshwater discharge and was explained principally by water temperature and salinity, rather than tidal height. Diel tidal effects were in play only at a neap tide in the wet season after no freshwater had been discharged for 17 days, which is rare during the wet season. These findings imply that episodic anthropogenic freshwater discharge events disturb predictable macrotidal effects on water column processes, in turn enhancing the ecological complexity of estuaries such as the Yeongsan River estuary that have previously been altered by engineered structures.

Advances in 4D Seismic and Geophysical Monitoring of Deepwater Fields

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 27828, “Advances in 4D Seismic and Geophysical Monitoring of Deepwater Fields,” by Kanglin Wang, Paul Hatchell, David Chalenski, and Jorge Lopez, Shell, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. Integrated surveillance is critical for understanding reservoir dynamics and improving field management. A key component of the surveillance is areal monitoring of subsurface changes by use of time-lapse geophysical surveys such as 4D seismic. The complete paper reviews the advances in these technologies with recent examples from the Gulf of Mexico (GOM) and deepwater Brazil. Data-Quality Improvement 4D seismic has played a pivotal role in monitoring offshore fields for some time. However, until recently, its application in the GOM had been limited, largely because the effects of the Loop Current and infrastructures make it difficult to repeat the feathering of streamers used in conventional 4D-seismic acquisition. The key for 4D success is to repeat everything in baseline and monitor surveys to make sure the time-lapse difference observed in the data reflects real subsurface changes rather than differences in data-acquisition conditions or processing work flows. To solve the challenge of streamer-positioning repeatability, an operator used ocean-bottom nodes (OBNs) to achieve highly repeated surveys at the Mars Field, and excellent 4D results were obtained. Since then, 4D seismic has been deployed successfully at the portfolio scale in the GOM and that operator’s 4D surveillance strategy has been changed from streamer seismic to ocean-bottom seismic (OBS), which includes OBNs and ocean-bottom cables. In addition to source and receiver positions, other conditions in data acquisition can play important roles in 4D repeatability—for example, the variation of water properties during a seismic survey and between different surveys including water depth (tides) and seismic velocity in water. Such variations have been a well-known issue that limits the repeatability of 4D seismic, in particular for OBS data where multiple migration is often used. Seismic travel-time analysis is traditionally used to estimate errors and make corrections, but the process is often complicated by coupled factors including tides, water velocities, positioning errors, and the clock drift of OBNs, which collectively make it difficult to achieve precise water static corrections. To address this challenge, a seafloor device called the Pressure Inverted Echo Sounder (PIES) was developed for direct measurement and continuous monitoring of water- column properties during marine seismic surveys. A PIES is deployed at the seafloor and monitors two-way water time by transmitting an acoustic signal and measuring the time it takes to be reflected back from the surface. Such information has been used to make travel-time corrections of seismic data for enhanced data repeatability in the operator’s 4D processing projects.

The Effect of Alongcoast Advection on Pacific Northwest Shelf and Slope Water Properties in Relation to Upwelling Variability.

The Northern California Current System experiences highly variable seasonal upwelling in addition to larger basin‐scale variability, both of which can significantly affect its water chemistry. Salinity and temperature fields from a 7 year ROMS hindcast model of this region (43°N–50°N), along with extensive particle tracking, were used to study interannual variability in water properties over both the upper slope and the midshelf bottom. Variation in slope water properties was an order of magnitude smaller than on the shelf. Furthermore, the primary relationship between temperature and salinity anomalies in midshelf bottom water consisted of variation in density (cold/salty versus warm/fresh), nearly orthogonal to the anomalies along density levels (cold/fresh versus warm/salty) observed on the upper slope. These midshelf anomalies were well‐explained (R 2 = 0.6) by the combination of interannual variability in local and remote alongshore wind stress, and depth of the California Undercurrent (CUC) core. Lagrangian analysis of upper slope and midshelf bottom water shows that both are affected simultaneously by large‐scale alongcoast advection of water through the northern and southern boundaries. The amplitude of anomalies in bottom oxygen and dissolved inorganic carbon (DIC) on the shelf associated with upwelling variability are larger than those associated with typical variation in alongcoast advection, and are comparable to observed anomalies in this region. However, a large northern intrusion event in 2004 illustrates that particular, large‐scale alongcoast advection anomalies can be just as effective as upwelling variability in changing shelf water properties on the interannual scale.

Dissolution Rates of Actinolite in Water and Its Modified Mineral Surface Across the Critical State

Dissolution kinetic experiments of actinolite in water were performed using a flow-through reactor at temperatures from 20 to 400 °C and 23.5±0.5 MPa. The results indicate that the steady-state release rates of the different elements of actinolite vary with temperature. Generally, Ca, Mg, Fe, and Al dissolve more quickly than Si at temperatures from 20 °C to near 300 °C, but slower from 300 to 400 °C. The Si release rate increases with temperatures from 20 to 300 °C and then decreases from 300 to 400 °C. Si release rate reaches the maximum at 300 °C. Amorphous Si-rich surface layers occur at temperature 300 °C. Water property variations within the critical region strongly affect the dissolution rates and the modification of surface.

Seasonal and geographical distribution of near-surface small photosynthetic eukaryotes in the western North Pacific determined by pyrosequencing of 18S rDNA.

In this study, we investigated the distribution of small photosynthetic eukaryotes in the near-surface layer of the western North Pacific at four stations, including two oceanic stations where the subarctic Oyashio and subtropical Kuroshio currents influence a transition region and the bay mouth and head of the Sendai Bay, from April 2012 to May 2013. Flow cytometry was applied to sort small photosynthetic eukaryotes (<5 μm), and high-throughput sequencing of 18S rDNA was performed. Our taxonomic analysis showed that 19/195 operational taxonomic units (OTUs) were frequently distributed among all sites. Composition analysis showed that the OTUs had characteristic patterns and were divided into four main groups. Two groups reflected the low-saline water and winter season, with the characteristic OTUs belonging to diatoms; Chaetoceros and Leptocylindrus were characteristic of low saline water, and two diatom genera (Minidiscus and Minutocellus) and Cryptomonadales-related OTUs were prevalent in the winter. Our results indicate that the community composition of small photosynthetic eukaryotes seasonally changes in a dynamic manner according to variations in water properties.

Alongcoast structure and interannual variability of seasonal midshelf water properties and velocity in the Northern California Current System

AbstractMoored sensors were maintained for ∼5 years on the northern California Current System (CCS) midshelf. The alongcoast sensor array spanned the area of influence of the plume from the Columbia River, several submarine canyons, as well as a coastal promontory where the equatorward coastal jet frequently separates from the shelf. Upwelling‐favorable wind stress magnitude decreases poleward by more than a factor of three over the latitudinal range and shelf width varies by a factor of two. In spite of the alongcoast structure in setting, both seasonal and interannual patterns in subsurface layer water properties were remarkably similar at all sites. Higher in the water column, freshwater forcing was substantial. Because of the near surface freshwater input, seasonal sea surface and subsurface temperatures were almost perfectly out of phase in the northernmost CCS, with a mid water column inversion in winter. Year to year differences in subsurface layer wintertime water properties were similar to spatial and temporal patterns of wind stress variability: little alongcoast structure except in salinity, but pronounced interannual differences strongly related to local wind stress. Summertime wind and subsurface property patterns were the opposite of those in winter: pronounced alongcoast wind stress structure, but little or no alongcoast or interannual variability in water properties, and only a weak relationship to local wind stress. Summertime interannual water property variability, including source waters, was shown to be more consistent with “remote forcing” via larger scale wind stress rather than with local wind stress, particularly in the northernmost CCS.

Variability in water properties and predictability of sea surface temperature along Sanriku coast, Japan

We investigated the main controlling factors and predictability of extreme sea surface temperature changes along the Sanriku coast (the east coast of the northern part of Japan's main island). We analyzed distributions of water properties and flow fields via intensive observations using a conductivity–temperature–depth profiler and a coastal water-temperature monitoring system from January 1998 to December 2012. Satellite altimetry and tide gauge data were also analyzed to investigate more widespread horizontal and temporal variation of the sea surface flow field. Anomalous temperature events (2°C lower and higher than climatological monthly values) were observed in winter 2006 and fall 2010 and 2012 along the Sanriku coast. In winter (fall) 2006 (2010, 2012), we observed both unusually thick and wide cold/fresh (warm/saline) waters, corresponding to the Oyashio (Tsugaru Warm Current) waters. At that time, sea surface velocities of the Oyashio (Tsugaru Warm Current) along the Hokkaido coast (Tsugaru Strait) were also high. We propose new methods for predicting extreme temperature changes a few months in advance, based on current observations.

Water retention of the loess-derived Luvisols with lamellic illuvial horizon in the Trzebnica Hills (SW Poland)

Abstract The aim of work was to characterize the water retention in the silt-textured Luvisols with lamellic illuvial horizon (argic) that occur in the loess covered northern part of the Silesian Lowland. Soil pits were localized on the Trzebnica Hills near the villages: Machnice (profile 1), Skarszyn (profile 2) and Zaprężyn (profile 3 and 4). Profiles Machnice 1 and Skarszyn 2 were situated in the upper parts of the hills covered with beech stands with an admixture of oak, linden and maple. Profiles Zaprężyn 3 and 4 were situated in the central and lower parts of the arable slope. During the field work conducted in April 2011, 29 soil samples were collected for texture, bulk density and water properties analysis. The soils under study were characterized by texture of silt loam with lower clay content in humus horizons (.loamy silt. according to Polish classification), and higher clay content (.clayey silt.) in the illuvial and subsoil horizons. The texture of all examined profiles was dominated by the „loess“ fractions. Variable abundance of the massive lamellae causes variations in water properties of the illuvial (sub-)horizons. It was found that lamellic illuvial horizons in the loess-derived Luvisols have higher field water capacity than the homogenous illuvial horizons, apart of the clay content. There was no apparent effect of the horizon kind (homogeneous versus lamellic) on the soil bulk density. These properties mainly depended on the total clay content in a particular horizon (sub-horizon).

Hydrographic variability over the northeastern Chukchi Sea shelf in summer-fall 2008–2010

We used shipboard CTD, mooring, meteorological, glider, and high-frequency radar data to examine spatial and temporal (seasonal and interannual) variations in the circulation and water properties over the central portion of the northeastern Chukchi Sea shelf from August–October of 2008, 2009, and 2010. Seasonally, warm and moderately saline Bering Sea Water (BSW) replaces cool, dilute surface meltwaters and cold, saline, sub-surface, winter-formed waters. BSW advection thus affects shelf stratification and the heat budget with oceanic heat flux convergence supplanting solar heating as the dominant shelf heat source by September. BSW spreads eastward from the Chukchi's Central Channel, so that water property and stratification transitions proceed from west to east across the study region. Models predict a mean clockwise flow around Hanna Shoal (which lies to the north of the study area) suggesting winter-formed waters from northeast of the Shoal are advected southwestward into a portion of the study area. The observations, though limited, support this notion. We hypothesize that the convergence of BSW from the west and winter waters from the northeast leads, in some years, to large horizontal variations in water properties, stratification, and ocean heat flux convergence over spatial scales of ~50–100km.Interannual variations in summer/fall shelf water properties appear linked to processes occurring in the Bering and/or southern Chukchi Sea, and the regional winds (which affect the local circulation). Although there were large interannual differences in shelf-wide ice retreat patterns from May–July, these differences were not reflected in late summer water properties.

Assessment of Spatial Structure of Groundwater Quality Variables Based on the Geostatistical Simulation

Our main objective in the present study was to assess the spatial variation of chemical and physical water properties. Prior to the design of groundwater quality monitoring networks, it is essential to investigate the spatial structure of the groundwater quality variables. A case study is presented which used ground water quality observations from groundwater domestic wells in the Dameghan, Iran. The anslyses of the spatial structure used the following variables: Electrical Conductivity (EC), PH, SAR, TDS, Sodium (Na), Calcium (Ca), Magnesium (Mg). For all these variables the spatial structure is described by means of geostatistical simulation, used to yield a series of stochastic images characterized by equally probable spatial distributions of the chemical and physical water properties across the area. The data set including 5 years of annual observations. At first normality and homogeneity of data are examined. Then variographic analysisusing two techniques including kriging, Weighted Moving Average (WMA) were applied for presenting spatial variation of water properties. Finally comparison of the results using statistical techniques showed that for more groundwater quality variables (e.g. TDS, EC, Cation, Na, Ca) kriging technique performed better than WMA-2 technique in characterizing the spatial variability. WMA-2 technique only for some groundwater quality variables like SAR and Mg has better result than kriging to simulate groundwater quality variables.

Long-term variations of surface and intermediate waters in the southern Indian Ocean along 32°S

Variations of water properties in surface and intermediate layers along 32°S in the southern Indian Ocean were examined using a 50-year (1960–2010) time series reproduced from historical hydrographic and Argo data by using optimum interpolation. Salinity in the 26.7–27.3σθ density layer decreased significantly over the whole section, at a maximum rate of 0.02 decade−1 at 26.8–26.9σθ, for the 50-year average. Three deoxygenating cores were identified east of 75°E, and the increasing rate of apparent oxygen utilization in the most prominent core (26.9–27.0σθ) exceeded 0.05 ml l−1 decade−1. The pycnostad core of Subantarctic Mode Water (SAMW) and the salinity minimum of Antarctic Intermediate Water shifted slightly toward the lighter layers. Comparisons with trans-Indian Ocean survey data from 1936 suggest that the tendencies found in the time series began before 1960. Interestingly, cores of many prominent trends were located just offshore of Australia at 26.7–27.0σθ, which is in the SAMW density range. Spectrum analysis revealed that two oscillation components with time scales of about 40 and 10 years were dominant in the subsurface layers. Our results are fairly consistent with, and thus support, the oceanic responses in the southern Indian Ocean to anthropogenic climate change predicted by model studies.

2006~2010년 기간 동안 대한해협 서수도에서 관측된 해수 물성의 변동

Seasonal to inter-annual variations of water properties in the western channel of the Korea Strait are investigated using quasi-monthly hydrographic observations collected during 2006-2010. Weak vertical temperature and salinity gradients are observed during the winter months and these remain until May. At the upper layer, temperature increases from March and reaches a maximum in August, while salinity decreases during the same period. Near-bottom water shows low temperatures during late winter and fall with a minimum peak in September. Korea Strait Bottom Cold Water produces thick layers (>20 m) in 2006 and 2010, while it is observed very near the bottom with relatively high temperature in 2008 and 2009.

Soil water property variations in three adjacent land use types in the Rift Valley area of Ethiopia

This study investigated the effects of land use change on infiltration and moisture content of soils in three land use types. A total of 81 soil and core samples (3 replications × 3 treatments × 3 profiles × 3 soil depths) were used to determine parameters that may affect the infiltration properties of soils. The infiltration rate was measured in the field using double-ring infiltrometer with three replicates in each land use type. Results showed that infiltration rates were generally slow in the open grazed and cultivated lands suggesting high potential for runoff, limited percolation, and very low amount of water available in the soil profiles. The accumulated infiltration in soils under cultivation and open-grazing was smaller than the controlled grazing by approximately 57%. Similarly, cultivation and open-grazing had reduced the soil moisture content by 29 and 33%, respectively, compared to the controlled grazing. Surface soil compaction, higher dry bulk density and lower soil organic carbon, appeared to be the principal factors for the low infiltration capacity and moisture content of the soils. Therefore, dry land management, with long term tree cover and well regulated grazing system, is very crucial for the sustainable ecosystem functioning of this environmentally fragile area.

새만금 방조제 완공 이전 만경강 하구역 식물플랑크톤 군집의 주기적인 변동

Eutrophicated water fed through Mankyeong River and Dongjin River into the new Saemankeum Lakemight seriously affect the water quality and phytoplankton community in the lake. To obtain control reference data for the later studies on environmental changes due to the construction of the Saemankeum Sea Wall, we performed a monthly investigation on the physico-chemical properties of the water and phytoplankton community at 3 stations in the Mankyeong River Estuary over 14 months starting from September 1999. Water temperature ranged from 0.3~32.9℃ due to the typical seasonal variations in temperate on the coasts and salinity exhibited a wide annual range of 0.2~33.7 psu along with regular and huge hourly variations according to tidal cycles. Inorganic nutrients were supplied from rivers to the monitoring station and the whole lake. The average concentration of total-N, 6.99 mgㆍl?¹, was higher than the water quality for agricultural use with peak values occurring in winter. Species composition showed a seasonal succession pattern, where a high diversity was observedin summer and autumn and vice versa in winter. Hourly variations of water properties in the “Mankyeong bridge” Station were quite regular and well in accordance with the daily tidal cycles. The different degree of sea water intrusion during the flood tide at each of the 3 stations exhibited a different range and variation pattern of water temperature and salinity throughout a day. Hourly changes in species composition were in harmony with the daily tidal cycles, resulting in extremely variable spatio-temporal variation.