Contrasting nutrient exports from a forested and an agricultural catchment in south-eastern Australia

Dissolved organic carbon (DOC) and total and inorganic nitrogen and phosphorus concentrations were determined over 3 years in headwater streams draining two adjacent catchments. The catchments are currently under different land use; pasture/grazing vs plantation forestry. The objectives of the work were to quantify C and nutrient export from these landuses and elucidate the factors regulating export. In both catchments, stream water dissolved inorganic nutrient concentrations exhibited strong seasonal variations. Concentrations were highest during runoff events in late summer and autumn and rapidly declined as discharge increased during winter and spring. The annual variation of stream water N and P concentrations indicated that these nutrients accumulated in the catchments during dry summer periods and were flushed to the streams during autumn storm events. By contrast, stream water DOC concentrations did not exhibit seasonal variation. Higher DOC and NO₃ ⁻ concentrations were observed in the stream of the forest catchment, reflecting greater input and subsequent breakdown of leaf-litter in the forest catchment. Annual export of DOC was lower from the forested catchment due to the reduced discharge from this catchment. In contrast however, annual export of nitrate was higher from the forest catchment suggesting that there was an additional NO₃ ⁻ source or reduction of a NO₃ ⁻ sink. We hypothesize that the denitrification capacity of the forested catchment has been significantly reduced as a consequence of increased evapotranspiration and subsequent decrease in streamflow and associated reduction in the near stream saturated area.     

3H-mepyramine binding to histamine H1-receptors in guinea pig lung: Characteristics and regulation by ions

The antogonist [³H]-mepyramine is used to label histamine H₁-receptors in guinea pig lung. Scatchard analysis reveals two classes of binding sites. Monovalent cations decrease steady-state binding (Na⁺ > Li⁺ > K⁺), while divalent cations (Mg⁺⁺, Ca⁺⁺, Mn⁺⁺, Ba⁺⁺) exhibit a biphasic curve, increasing binding at low concentrations and decreasing it at higher levels. Na⁺ decreases both affinity and number of binding sites. Dissociation curve shows two components, and Na⁺ accelerates the rate of dissociation of the slower component. GTP does not affect the binding of the antagonist ³H-Mepyramine.     

LETTER TO THE EDITOR

SUMMARY

A two-year limnological survey between 1973 and 1975 showed that the Roodeplaat Dam is a warm monomictic impoundment which has stable thermal stratification during summer. Oxygen supersaturation of the surface waters and anaerobic conditions in the hypolimnion were encountered during summer. Water transparency was seasonal and related to existing phytoplankton populations and allochthonously-introduced clay material. Chemical stratification during summer was prominent and appeared to be caused not only by mineralization processes in the hypolimnion, but also by dilution in the surface layers during summer flooding. Because of the morphometry of the impoundment and the fact that sewage effluents are discharged into the major inflow, considerable horizontal variation in most chemical and biological characteristics was found. On the basis of the nutrient content of the waters and the magnitude of the phytoplankton populations observed, Roodeplaat Dam may be classified as a highly eutrophic water body.     

HYDROCHEMISTRY OF THE UPPER ORANGE RIVER CATCHMENT

SUMMARY

A four year pre-impoundment study of the catchment of the Hendrik Verwoerd Dam was conducted. The Orange River was the major source of dissolved chemicals and suspended sediments, while the Caledon River contributed 24 and 30% respectively, and the Kraai River 9 and 8% respectively. The upper reaches of the Orange River catchment contributed mainly to the dissolved chemical and sediment loads, in contrast to the minimal contribution of the lower reaches. This was in spite of the relatively stable geological formations in the upper reaches and the erodable formations in the lower reaches. Dry-wet seasonal variations occurred in nutrient and sediment concentrations and loads, except for the Bell River where constant values were measured. The water was characterized by magnesium and bicarbonate dominance. Adsorption by the suspended sediments was dominated by calcium (potassium in the Bell River) and zinc among the trace elements. Due to its low salinity and sodium adsorption ratio, the water was suitable for irrigation. High magnesium levels made it, however, less attractive for irrigational purposes.

The phosphorus loading rate at the inflow of the Hendrik Verwoerd Dam was only 0,55 g P m^?2 a^?1, which was well below the 1,39 g P m^?2 a^?1 critical rate for eutrophic conditions, applying the Vollenweider Model. Therefore, this impoundment was classified as oligo-mesotrophic.     

Response of sugarcane to different types of salt stress

Summary Due to climatic conditions and prevailing water regime the yield and sucrose recovery in sugarcane are high in South Western India. However, excessive irrigation, poor drainage and luxuriant use of fertilizers have resulted in conversion of large fertile areas into saline lands. The salinity is due to the excess of Na⁺, Ca⁺⁺, Mg⁺⁺, SO₄ ^– and Cl^– ions. Individual salts of NaCl, Na₂SO₄, MgCl₂ and MgSO₄ were employed in culture experiments to study salt stress effect on sugarcane variety Co 740. It was observed that sulphate salinity was more toxic to sugarcane than the chloride one. Sulphate salts caused more inhibition of growth, chlorophyll synthesis, PEPCase activity, decreased the uptake of K⁺ and Ca⁺⁺ ions but stimulated nitrate reductase. The stress did not result in proline accumulation in the sugarcane cultivar Co 740. The degree of toxicity of different ions in decreasing order in sugarcane cultivar Co 740 is SO₄ ^–>Na⁺>Cl^–>Mg⁺⁺.     

Effects of Catchment and Riparian Landscape Setting on Water Chemistry and Seasonal Evolution of Water Quality in the Upper Han River Basin,China

Six-year (2005–2010) evolution of water chemistry (Cl⁻, NO₃ ⁻, SO₄ ²⁻, HCO₃ ⁻, Na⁺, K⁺, Ca²⁺ and Mg²⁺) and their interactions with morphological properties (i.e., slope and area), land cover, and hydrological seasonality were examined to identify controlling factors and processes governing patterns of stream water quality in the upper Han River, China. Correlation analysis and stepwise multiple regression models revealed significant correlations between ions (i.e., Cl⁻, SO₄ ²⁻, Na⁺ and K⁺) and land cover (i.e., vegetation and bare land) over the entire catchment in both high- and low-flow periods, and in the buffer zone the correlation was much more stronger in the low-flow period. Catchment with steeper slope (>15°) was negatively correlated with major ions, largely due to multicollinearity of basin characteristics. Land cover within the buffer zone explained slightly less of major elements than at catchment scale in the rainy season, whereas in the dry season, land cover along the river networks in particular this within 100 m riparian zone much better explained major elements rather than this over the entire catchment. Anthropogenic land uses (i.e., urban and agriculture) however could not explain water chemical variables, albeit EC, TDS, anthropogenic markers (Cl⁻, NO₃ ⁻, SO₄ ²), Na⁺, K⁺ and Ca²⁺ significantly increased during 2005–2010, which was corroborated by principal component analyses (PCA) that indicated anthropogenic inputs. Observations demonstrated much higher solute concentrations in the industrial-polluted river. Our results suggested that seasonal evolution of water quality in combined with spatial analysis at multiple scales should be a vital part of identifying the controls on spatio-temporal patterns of water quality.     

NOTES ON THE AVAILABILITY AND CHEMICAL COMPOSITION OF WATER FROM THE GRAVEL PLAINS OF THE NAMIB-NAUKLUFT PARK

SUMMARY

Data are presented on the occurrence of a surprising number of permanent water sources on the gravel plains of the Namib-Naukluft Park, South West Africa. As a consequence, no game animal is further than ca 25 km away from the nearest watering-place. Within a broad range of ionic contents, the surface waters of the desert display a marked similarity in their chemical composition, being mainly dominated by Na⁺>Ca⁺⁺>Mg⁺⁺: Cl^?>SO₄ ^?>HCO₃ ^??CO_3- ^?. Evaporation, precipitation and rock dominance seem to be the main controlling mechanisms involved in determining the chemical composition of the waters.     

Role of external calcium in sodium and chloride transport in the gills of seawater-adaptedMugil capito

Summary When the mulletMugil capito is transferred to medium lacking Ca⁺⁺ (either Ca⁺⁺-free seawater or distilled water) the passive permeability of the gill to Na⁺ and Cl^– is increased and the activating effect of external K⁺ on the Na⁺ and Cl^– effluxes in hyposaline media is inhibited. The permeability of the gill increases progressively in proportion to the time of Ca⁺⁺ deprivation; it declines when Ca⁺⁺ is added again to the external medium. The active mechanisms for ion excretion are not reversible. At external Ca⁺⁺ concentrations from 0.1 to 10 mM the Na⁺ permeability is constant but the activation of Na⁺ efflux by K⁺ shows a maximum at a Ca⁺⁺ concentration of about 1 mM. For activation of Cl^– efflux external bicarbonate must be present, in addition to Ca⁺⁺, suggesting the existence of a Cl^–/HCO ₃ ^– exchange. The mechanism by which Ca⁺⁺ controls the passive branchial permeability is thus probably different from that involved in K⁺ activation of ion excretion. The Ca⁺⁺ effect on the K⁺ sensitive ionic excretory mechanisms seems to be related to intracellular Ca⁺⁺ movements. Thus, on the one hand, substances such as Ruthenium Red and La⁺⁺⁺ which both inhibit Ca⁺⁺ exchange, in media containing Ca⁺⁺ and HCO ₃ ^– also inhibit K⁺ activation of Na⁺ and Cl^– effluxes; on the other hand, the ionophore A 23187, a stimulator of Ca⁺⁺ exchange, when added to these media, activates the Na⁺ and Cl^– effluxes; its maximal effect on the Na⁺ flux occurs at 2 mM Ca⁺⁺.Abbreviations ASW-Ca artificial seawater minus calcium - DW deionised water - DWCa deionised water with 1 mM Ca⁺⁺ added - DWCaHCO ₃ DW with calcium plus bicarbonate - DWHCO ₃ DW with 1 mM sodium bicarbonate added - FW freshwater (tap water) - FWK freshwater with K⁺ added - P. D. potential difference - SW seawater The experiments reported in this paper were done with Jean Maetz who tragically died in August 1977. It is the last report about several years of friendly collaboration     

Some Physical and Chemical Properties of Water from an Undisturbed Tropical Catchment Area (Guma Dam,Sierra Leone)

The water had a very low content of total suspended solids (<1 mg l⁻¹), but its transparency was high (5–8 Hazen units). The concentration of Mg⁺⁺ and Ca⁺⁺ were below 1 mg l⁻¹, but that of SiO₂ was 5.3 mg l⁻¹. Free CO₂ was abundant (15.3 mg l⁻¹) and the pH was low (<6.5). These conditions were accompanied by low concentrations of PO₄-P, total iron and NO₃-N. The DO content of the water was always below 80 %, but the chloride concentration (8.4 mg l⁻¹) seems relatively high for this type of freshwaters. It is, however, much lower than that known for arid areas. It is concluded that the geology and vegetation dominate the chemistry of the water from the Guma Dam catchment area. The influence of man is acknowledged only in as far as he has protected the catchment area.     

THE LIMNOLOGY OF SOME SOUTH AFRICAN IMPOUNDMENTS I. THE PHYSICO-CHEMICAL LIMNOLOGY OF HARTBEESPOORT DAM

SUMMARY

Hartbeespoort Dam is a eutrophic, warm monomictic lake with overturn occurring in April. The lake is stratified for about six months of the year and in late summer the stratification appears stable. Light penetration in the dam depends both on the inflow of turbid water as well as on the magnitude of the algal population. In summer the surface waters are often super-saturated with oxygen, whilst the hype limnion is anaerobic. The concentrations of nitrogen compounds, phosphate, Na, K, Ca, CI and SO₄ are higher in waters entering the dam via the Crocodile River. Nitrogen compounds arc the primary growth-limiting nutrients for algal growth and phosphate is the secondary growth-limiting nutrient. Phosphate concentrations in the water have increased approximately a hundredfold since 1928 and NO₃ ?N concentrations about threefold. The pH as well as the mineral content of the dam have also increased over the last 50 years.     

Vertical pattern and its driving factors in soil extracellular enzyme activity and stoichiometry along mountain grassland belts

Headwater streams are foci for nutrient and energy loading from terrestrial landscapes, in situ nutrient transformations, and downstream transport. Despite the prominent role that headwater streams can have in regulating downstream water quality, the relative importance of processes that can influence nutrient uptake have not been fully compared in heterotrophic aquatic systems. To address this research need, we assessed the seasonality of dissolved organic carbon (DOC) and nitrate (NO₃^?) uptake, compared the relative influence of hydrologic and biogeochemical drivers on observed seasonal trends in nutrient uptake, and estimated the influence of these biological transformations on watershed scale nutrient retention and export. We determined that seasonal reductions in DOC and NO₃^? concentrations led to decreases in the potential for the biotic community to take up nutrients, and that seasonality of DOC and NO₃^? uptake was consistent with the seasonal dynamics of ecosystem metabolism. We calculated that that during the post-snowmelt period (June to August), biotic retention of both dissolved organic carbon and nitrate exceeded export fluxes from this headwater catchment, highlighting the potential for biological processes to regulate downstream water quality.     

Carbon Dioxide Variation in a Hardwood Forest Stream: An Integrative Measure of Whole Catchment Soil Respiration

The concentration of CO₂ in stream water is a product of not only instream metabolism but also upland, riparian, and groundwater processes and as such can provide an integrative measure of whole catchment soil respiration. Using a 5-year dataset of pH, alkalinity, Ca²⁺, and Mg²⁺ in surface water of the West Fork of Walker Branch in eastern Tennessee in conjunction with a hydrological flowpath chemistry model, we investigated how CO₂ concentrations and respiration rates in stream, bedrock, and soil environments vary seasonally and interannually. Dissolved inorganic carbon concentration was highest in summer and autumn (P < 0.05) although the proportion as free CO₂ (pCO₂) did not vary seasonally (P > 0.05). Over the 5 years, pCO₂ was always supersaturated with respect to the atmosphere ranging from 374 to 3626 ppmv (1.0- to 10.1-fold greater than atmospheric equilibrium), and CO₂ evasion from the stream to the atmosphere ranged from 146 to 353 mmol m⁻² d⁻¹. Whereas pCO₂ in surface water exhibited little intra-annual or interannual variation, distinct seasonal patterns in soil and bedrock pCO₂ were revealed by the catchment CO₂ model. Seasonally, soil pCO₂ increased from a winter low of 8167 ppmv to a summer high of 27,068 ppmv. Driven by the seasonal variation in gas levels, evasion of CO₂ from soils to the atmosphere ranged from 83 mmol m⁻² d⁻¹ in winter to 287 mmol m⁻² d⁻¹ in summer. The seasonal variation in soil CO₂ tracked soil temperature (r ²= 0.46, P < 0.001) and model-derived estimates of CO₂ evasion rate from soils agreed with previously reported fluxes measured using chambers (Pearson correlation coefficient = 0.62, P < 0.05) supporting the model assumptions. Although rates of CO₂ evasion were similar between the stream and soils, the overall rate of evasion from the channel was only 0.4% of the 70,752 mol/d that evaded from soils due to the vastly different areas of the two subsystems. Our model provides a means to assess whole catchment CO₂ dynamics from easily collected and measured stream-water samples and an approach to study catchment scale variation in soil ecosystem respiration. Received 24 July 1997; accepted 14 November 1997.     

Fire and soil-plant nutrient relations in a pine-wiregrass savanna on the coastal plain of North Carolina

Summary Changes in soil and plant nutrient conditions were evaluated following various burn and clip treatments in a longleaf pine-wiregrass savanna in Bladen Co., N.C., USA. Ground fires were found to add substantial quantities of N, P, K, Ca, and Mg to the soil, though not necessarily in forms immediately available to plants. Less than 1% of the total nitrogen in the charred residue (ash) is present as nitrate or ammonium. Considerable quantities of all nutrients examined were lost to the atmosphere during burning. Green leaf tissue in recently burned areas was consistently higher in N, P, K, Ca, and Mg compared to unburned areas. Howerver, when compared to similar tissues from clipped plots, burned area tissues were significantly higher in N, Ca, and Mg only. Data presented here suggest that tissue age significantly affects nutrient content and must be considered in any analysis of tissue nutrient content following burning. Within 4–6 months following fire, burned-area tissue nutrient content decreases to concentrations found in the unburned area. Burning resulted in initial enrichment of available soil nutrients including PO₄, K⁺, Ca⁺⁺, and Mg⁺⁺, however, NO₃ ^-, and NH₄ ⁺ concentrations in burned soil were not significantly different from unbruned soil. Soil and plant nutrient changes in an area burned two years in succession indicate that repeated burning may diminish nutrient availability. Plant response to various nutrient enrichment treatments of the soil indicated that nitrogen is limiting growth in both burned and unburned soils and that burning may alter some factors other than nutrients which may retard plant growth in unburned areas.     

The influence of catchment characteristics on the seasonality of carbon and nitrogen species concentrations in upland rivers of Northern Scotland

Data from 13 catchments with no arable land in Northern Scotland were used to develop empirical linear regression models of average monthly NO₃ ^? concentrations and average summer and winter concentrations for NH₄ ⁺, dissolved organic N (DON) and dissolved organic carbon (DOC) as a function of catchment characteristics. All catchments displayed a pronounced seasonal NO₃ ^? cycle. Variation in monthly mean NO₃ ^? concentration within and between catchments could be predicted from mean monthly air temperature using separate regression equations for temperatures < and ≥ 5 °C. Soil type, climate and land use influenced NH₄ ⁺ concentrations. In summer, concentrations of NH₄ ⁺ were largest in catchments with extensive areas of brown forest soils, which are less acidic and more base-rich than other upland soils. However, concentrations declined with increasing conifer cover and summer rainfall. In winter, however, % conifer cover had a positive effect, while higher temperature and higher humus iron podzol cover had negative influences. DON concentration decreased with increasing catchment elevation in both summer and winter. Surprisingly, concentrations of DON only displayed a positive relationship with percentage peat cover in the summer. The most important factor controlling DOC concentration was soil type, with a positive relationship being observed between DOC and peat and humus iron podzol coverage. Elevation was also important, but only in the winter when concentrations were negatively correlated with maximum catchment elevation. Overall, multivariate regression equations explained the spatial and seasonal variability in N species concentrations over a range of catchments within Northern Scotland.     

Inter-annual,Annual, and Seasonal Variation of P and N Retention in a Perennial and an Intermittent Stream

Headwater streams represent the key sites of nutrient retention, but little is known about temporal variation in this important process. We used monthly measurements over 2 years to examine variation in retention of soluble reactive phosphorus (SRP) and ammonium (NH₄⁺) in two Mediterranean headwater streams with contrasting hydrological regimes (that is, perennial versus intermittent). Differences in retention between streams were more evident for NH₄⁺, likely due to strong differences in the potential for nitrogen limitation. In both streams, nutrient-retention efficiency was negatively influenced by abrupt discharge changes, whereas gradual seasonal changes in SRP demand were partially controlled by riparian vegetation dynamics through changes in organic matter and light availability. Nutrient concentrations were below saturation in the two streams; however, SRP demand increased relative to NH₄⁺ demand in the intermittent stream as the potential for phosphorus limitation increased (that is, higher dissolved inorganic nitrogen:SRP ratio). Unexpectedly, variability in nutrient retention was not greater in the intermittent stream, suggesting high resilience of biological communities responsible for nutrient uptake. Within-stream variability of all retention metrics, however, increased with increasing time scale. A review of studies addressing temporal variation of nutrient retention at different time scales supports this finding, indicating increasing variability of nutrient retention with concomitant increases in the variability of environmental factors from the diurnal to the inter-annual scale. Overall, this study emphasizes the significance of local climate conditions in regulating nutrient retention and points to potential effects of changes in land use and climate regimes on the functioning of stream ecosystems.     

筑坝扩容下高原湿地拉市海植物群落分布格局及其变化

基于遥感与地理信息系统技术、结合实地调查与验证,对高原湿地拉市海筑坝扩容13a来湿地植物群落类型、物种组成、空间分布格局进行研究,对比分析筑坝扩容前后植物群落变化特征。结果表明,拉市海当前分布有水葱 (Scirpus tabernaemontani)、两栖蓼 (Polygonum amphibium) 等2个挺水植物群落,鸭子草 (Potamogeton tepperi)、菱 (Trapa bispinosa)等2个浮叶植物群落,穗状狐尾藻 (Myriophyllum spicatum)、篦齿眼子菜 (Potamogeton pectinatus)、菹草 (Potamogeton crispus)、穿叶眼子草 (Potamogeton perfoliatus)、小叶眼子菜 (Potamogeton pusillns)等5个沉水植物群落,草甸植被分布于湖周。湿地植物物种共计61种,隶属于25科、48属,物种丰富度随沉水→浮叶→挺水→草甸逐渐增加。沉水植物群落分布面积最大(615.08 hm²),其次是草甸(214.60 hm²)、浮叶植物群落(140.01 hm²),挺水植物群落分布面积最小 (9.34 hm²),群落垂直层次随沉水→浮叶→挺水呈复杂化的趋势。筑坝13a来,拉市海植物群落类型从单一的沉水型植物群落发展成为由沉水、浮叶、挺水型组成的、水平空间多样化配置的湿地植被系统,其中穗状狐尾藻、篦齿眼子菜、小眼子菜等植物群落在筑坝蓄水13a后没有发生演替得以保留,而扇叶水毛茛(Butrachium bungei)、马来眼子菜(Potamogeton malaianus)和轮藻(Chara spp.)群落发生演替而消失。研究掌握了筑坝扩容下拉市海湿地植物群落分布格局及其变化特征,为科学评估筑坝蓄水对湿地生态系统的影响提供了基础性数据,同时也为水文改变下高原湿地生态系统的保护、管理以及资源可持续利用提供了一定的理论依据。     

Longitudinal and seasonal patterns of stream acidity in a headwater catchment on the Appalachian Plateau, West Virginia, U.S.A.

The chemical composition during baseflow was used to elucidate the fundamental processes controlling longitudinal and seasonal patterns of stream acidity in Yellow Creek, a chronically acidic headwater (pH range 3.7--4.2) on the Appalachian Plateau in northeastern West Virginia. Sulfate concentrations controlled the variability of stream acidity within the Yellow Creek catchment. Decreases in stream free H⁺ acidity with decreasing elevation likely resulted from SO ₄ ^2– retention in riparian wetland areas as well as spatial variation in dominant tree species. Seasonal variations in free H⁺ and inorganic monomeric aluminum (Alⁿ⁺) concentrations appeared related to seasonal fluctuations in baseflow discharge which was controlled by vegetative activity. Baseflow stream discharge, as well as H⁺ and Alⁿ⁺ acidity, gradually declined during the growing season (June through October), likely reflecting microbial SO ₄ ^2– > reduction in saturated anaerobic environments within riparian wetlands. A marked pulse of stream H⁺, Alⁿ⁺, and SO ₄ ^2– coincided with an abrupt increase in baseflow discharge resulting from the cessation of transpiration after leaf-fall in November. This seasonal pattern suggests that autumn may be a critical period for eastern brook trout in streams draining wetlands on the Appalachian Plateau.     

Seasonal dynamics of zooplankton in a shallow eutrophic,man-made hyposaline lake in Delhi (India): role of environmental factors

Old Fort Lake, a small (1.6 ha), shallow, and recreational water body in Delhi (India) was studied through monthly surveys in two consecutive years (January, 2000–December, 2001). Precipitation is the major source of water for this closed basin lake. In addition, ground water is used for replenishing the lake regularly. This alkaline, hyposaline hard water lake contains very high ionic concentration, especially of nitrates. Based on overall ionic composition, this lake can be categorized as chloride–sulfate alkaline waters with the anion sequence dominated by SO₄ ²⁻ > Cl⁻ > HCO₃ ⁻, and the cations by Mg⁺⁺ > Ca⁺⁺. The overall seasonal variability in physicochemical profile was largely regulated by the annual cycle of evaporation and precipitation, whereas the ground water largely influences its water quality. The lake exhibited phytoplankton-dominated turbid state due to dominance of the blue green alga, Microcystis aeruginosa. The persistent cyanobacterial blooms and the elevated nutrient levels are indicative of the cultural eutrophication of the lake. This study focuses on the relative importance of eutrophic vis-à-vis hyposaline conditions in determining the structure and seasonal dynamics of zooplankton species assemblages. A total of 52 zooplankton species were recorded and rotifers dominated the community structure qualitatively as well as quantitatively. The genus Brachionus comprised a significant component of zooplankton community with B. plicatilis as the most dominant species. The other common taxa were B. quadridentatus, B. angularis, Lecane grandis, L. thalera, L. punctata, Mesocyclops sp., and Alona rectangula. Multivariate data analysis techniques, Canonical Correspondence Analysis (CCA) along with Monte Carlo Permutation Tests were used to determine the minimum number of environmental factors that could explain statistically significant (P < 0.05) proportions of variation in the species data. The significant variables selected by CCA were NH₃–N followed by percent saturation of DO, COD, SS, BOD, NO₂–N, rainfall, silicates, and PO₄–P. The results indicate that the seasonal succession patterns of the zooplankton species were largely controlled by physicochemical factors related directly or indirectly to the process of eutrophication, whereas hyposaline conditions in the lake determined the characteristic species composition. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for Salt Lake Research     

Physicochemical limnology of the Tongue River Reservoir,Montana

A one year physicochemical survey was conducted on the Tongue River Reservoir, a run of the river impoundment in southeastern Montana. The Tongue River was the only significant inflow and supplied 93, 96 and 97% of the nutrient, major ion and water inputs to the impoundment. Heat advected from inflowing water accounted for 17% of the energy gained during the summer heating cycle. The annual nutrient load to the reservoir from the river was 20.2 g m^–2 total nitrogen (TN) and 3.8 g m^–2 total phosphorus (TP). Due to the absence of reducing conditions at depth and the complex seasonal pattern of water movement through the reservoir, 99% of the TN load was discharged but 49% of the TP load was retained in the reservoir.     

Implications of seasonal variation in nitrate export from forested ecosystems: a review from the hydrological perspective of ecosystem dynamics

In recent decades, the seasonal variation in NO₃ ^? discharge from forest ecosystems has been used increasingly by ecologists and hydrologists as a diagnostic indicator of the nutrient status of ecosystems. Major factors underlying the seasonal patterns of stream NO₃ ^? concentration include seasonal variations in (1) ecosystem nutrient demand, (2) solute transport capability of the hydrological condition, and (3) in-stream nutrient usage and supply. In this article I show how case studies have helped elucidate the dominant controlling factors by comparing data from Japanese catchments with previously compiled data from studies in North America and Europe. Moreover, I explain the different influences that hydrological and biogeochemical controls exert in regions with rainy (Japan) and dry (northeastern United States and Europe) summers. The seasonal variation in hydrological conditions is the predominant controlling factor in Japanese forests, whereas nutrient demand may predominate in the northeastern United States and Europe. I emphasize the importance of comparing seasonal patterns among regions with differing climates to obtain more universal explanations of seasonal variations in NO₃ ^?-related biogeochemical and hydrological dynamics in a forest ecosystem. In addition, multi-scale investigations will be needed to provide insight into the relative contributions of hillslope biogeochemical effects and in-stream biological activities.