An ecological investigation of the Myall Lakes region

This ecological study of the Myall Lakes, a lagoon system on the New South Wales central coast, presents the physical setting and characteristics of the Lakes’catchments and relates these characteristics to the hydrochemical features of surface and subsurface waters. In turn these hydrochemical features have been related to the aquatic communities. It is suggested that the predominance of forest vegetation and stable soils in the Lakes’catchment has assisted in retaining these lakes in a generally undisturbed state. Fluctuations of salinity, turbidity and ionic concentrations in the lower part of the system are controlled by natural inputs of rainfall, run-off and tidal flushings. However, Boolambayte Lake and particularly Myall Lake, the upper part of the system, appear to be isolated from these influences. The aquatic communities reflect these hydrochemical differences. The lack of flushing of waters in this upper part of the system, in Dirty Creek and to a lesser extent in the Myall River immediately upstream of the Broadwater, makes these areas particularly susceptible to pollution and eutrophication associated with increased development.     

Temporal and spatial variability in the phytoplankton community of Myall Lakes,Australia, and influences of salinity

The variability in the phytoplankton communities of the Myall Lakes, a series of four interconnected coastal lakes on the lower north coast of New South Wales, was studied between 1999 and 2002. There was considerable spatial variability across the lake system. Bombah Broadwater experienced blooms of Anabaena in 1999 and early 2000, but these were replaced from late 2000 onwards by Chroococcus and a variety of eukaryotic taxa, particularly flagellates and diatoms. In comparison, the phytoplankton community of Myall Lake was dominated for much of the study period by Chroococcus, Merismopedia and chlorophyte taxa. The sites located midway between these two main lakes represent an ecotone, with elements of the phytoplanktonic flora of both main lakes being present. Changes in phytoplankton community composition in Bombah Broadwater occurred fairly frequently. In contrast, the phytoplankton community in Myall Lake changed little during the course of the study and can be considered as being at long-term equilibrium. The reasons for this lie in the morphology and hydrology of the lake system, which in turn create gradients in a number of physico-chemical water quality attributes. Bombah Broadwater is influenced by episodic and stochastic freshwater inflows from the upper Myall River catchment, and in times of drought by saline marine incursions via the lower Myall River. Myall Lake however represents a cul-de-sac, with only a small hydraulic connection to the remainder of the lake system. As it has little input from its small catchment, the limnological conditions within this lake remain relatively constant for long periods of time. Although no patterns of seasonal succession were discernable in any of the lakes, some longer-term (annual) changes did occur, and certain taxa displayed enhanced growth in summer. Salinity was found to be an important factor in determining phytoplankton community composition and abundance. Canonical Correspondence Analysis of phytoplankton and environmental data for all sites combined, showed ammonia, total nitrogen and salinity (measured as electrical conductivity) to have the most influence on the phytoplankton community composition and abundance. Anabaena growth was positively related to ammonia concentration and negatively related to conductivity.     

Effects of increases in salinity on phytoplankton in the Broadwater of the Myall Lakes, NSW, Australia

The Broadwater of the Myall Lakes system is highly susceptible to cyanobacterial bloom formation after heavy rain events. During prolonged low flow periods, saline intrusion from the lower Myall River increases salinity levels and effectively controls some bloom forming algal taxa. To assess the effect of low-to-moderate increases in salinity (up to 4 ppt) on phytoplankton chlorophyll a, cell abundance, diversity and assemblage structure, salinity enhancement experiments were conducted on Broadwater samples collected in June 2005 (salinity 1.5 ppt), October 2005 (4 ppt) and January 2006 (12 ppt). Natural phytoplankton assemblages were incubated in the laboratory for 10 days, under different treatments of salinity (no addition, +2 ppt, + 4 ppt) and nutrient conditions (no addition, excess N+P). The greatest impact of salinity enhancement in N+P enriched samples was observed in June (1.5–5.5 ppt); chlorophyll a was significantly reduced in samples with the highest salinity treatment, and the taxon most negatively affected by an elevation in salinity to 5.5 ppt was Anabaena circinalis. Taxonomic richness and diversity (Shannon–Wiener index) were unexpectedly significantly higher at 5.5 ppt than at 1.5 ppt. This result, in part, explains the observed significant differences in phytoplankton assemblage structure over this salinity range. In October, the main effect of elevating salinity levels from 4 ppt to 8 ppt was a reduction in the abundance of chlorophytes, particularly Scenedesmus. Phytoplankton samples that were collected when the lake salinity level was 12 ppt were little affected by salinity increases of 2 ppt and 4 ppt, most likely because field samples were already relatively high in salt content. We suggest that further investigations focus on phytoplankton responses to salinity under a range of nutrient regimes that are common to coastal lakes.     

Temporal trends in plant species composition on mined sand dunes in Myall Lakes National Park,Australia

Abstract The floristic composition of the vegetation of mined and unmined sand dunes at Bridge Hill, in Myall Lakes National Park, was studied from 1982–90 inclusive. Data from mined sites ranging in age from 2–15 years post mining, with replication of time since mining in both time and space, were incorporated in the study. The mined part of the Bridge Hill dune is very different in plant species composition compared with either the dune prior to mining or to the adjacent unmined dunes. The mined dune also displays a temporal development of species composition over the period 2–15 years post mining, the dominant trend being a reduction in similarity to that of the dune prior to mining. Mining resulted in significant increases in the abundance of six introduced species, and in significant differences in the abundance of 49% of the native species. Species richness and diversity increased during the period 2–15 years post mining, and a significant component of this could be attributed to the presence of the introduced species.     

Nutrient and phytoplankton responses to a flood event in a series of interconnected coastal lakes: Myall Lakes Australia

Myall Lakes is a large brackish coastal lake on the east coast of Australia that was considered pristine until the occurrence of blue-green algal blooms in 1999. The temporal and spatial extent of chemical and biological changes to the water column of Myall Lakes was studied intensively after a rain event in 2002. Water quality profiles (T, EC, pH, DO), turbidity (secchi), nutrients (TN, NO _x , NH₄ ⁺, DON, TP, FRP, DOP, Si), and phytoplankton (chl a and cell counts) were measured at nine sites on eight occasions immediately after the rain event. Freshwater inflows affected a large area of the lake. Greatest changes were seen in areas close to the mouth of the upper Myall River which is the largest freshwater input to the lakes. Here, greatly elevated concentrations of NO _x , TP, and FRP (up to two orders of magnitude higher than background) were recorded immediately after the rain event but persisted for only 2 to 8 days. Slightly elevated concentrations of TP and NO _x were seen in inflows from the smaller Boolambayte Creek. Stratification was associated with bottom water anoxia and release of ammonia from the sediments. Identification of the sources of nutrient species delivered from different parts of the catchment, combined with studies of nutrient loads can assist managers to develop effective nutrient reduction strategies to reduce the incidence of blue-green algal blooms in Myall Lakes.     

Annual nutrient budget for an alpine grassland in the Garhwal Himalaya

Abstract. N, P and K dynamics were investigated in grazed and ungrazed alpine forb and grassy meadows in the Garhwal Himalaya. The growth forms examined were dwarf shrubs, forbs and graminoides. N, P and K contents were determined for various plant components and soil. The contribution of plant parts to the total vegetation capital of N, P and K was 20–33% (live shoot), 6–8% (dead shoot), 2–3% (litter) and 56–71% (root) in ungrazed plots, and 16–27, 6–7, 1–2, and 64–76% respectively in grazed plots. Grazing removed between 41–69% of total uptake of nutrients from the grassland. In protected areas, however, 65 to 81% of all nutrients were retained by the vegetation. This retention of nutrients is due to translocation to roots and rhizomes and is considered beneficial during grazing as it aids resprouting of the vegetation.     

Decomposition of dominant submerged macrophytes: implications for nutrient release in Myall Lake, NSW, Australia

Breakdown and nutrient dynamics of submerged macrophytes were studied in Myall Lake, Australia. Mass loss of Myriophyllum sulsagineum was the lowest (64.90%) among the studied macrophytes during the 322 days followed by charophytes (60.79%), whereas Najas marina and Vallisneria gigantea lost 91.15 and 86.02% of their respective initial mass during that time. The overall exponential breakdown rates of Najas marina and Vallisneria gigantea were similar, with k-values of 0.24 and 0.23 day⁻¹, respectively. These rates were significantly higher than the break down rates of charophytes (0.007 day⁻¹) and M. sulsagineum (0.008 day⁻¹). During growth phase, water column depicted lower nutrient concentrations while during decay period, significant increase in water column nutrients resulted. Release of nutrients from decomposing macrophytes and incorporation of these nutrients into sedimentary phase as well as uptake of nutrients by the growing macrophytes, can present a considerable cycling pathway of nutrients in Myall lake system. The results of this study suggest that different submerged macrophytes may differ appreciably in quality and may exhibit different decomposition rates, patterns and nutrient dynamics in aquatic ecosystems in general, and Myall lakes in particular.     

Holocene environmental change and development of the nutrient budget of histosols in North Iceland

Plant and Soil - Vegetation stabilizes slopes via root mechanical reinforcement and hydrologic reinforcement induced by transpiration. Most studies have focused on mechanical reinforcement and its...     

Groundwater contribution to the nutrient budget of Tomales Bay, California

Tomales Bay, a graben structure along the San Andreas Fault, was selected for modeling ecosystem nutrient dynamics because of its linear, one-dimensional morphology and relatively pristine state. Groundwater is a potentially important term in the nutrient budget. The geologic complexities created by the San Anreas Fault, however, complicate the hydrogeology and require the area to be subdivided into three regions: granite to the west, Franciscan Formation to the east, and alluvial fill in the trough. Nutrient concentrations in the groundwater were determined through extensive well sampling; groundwater discharge was estimated using both Darcy's Law calculations and a soil moisture budget. Results indicate that groundwater discharge is of the same order of magnitude as summer streamflow into the Bay, while being significantly less than other freshwater inputs in winter. Dissolved nutrient (phosphate, nitrate + nitrite, ammonium, silica and DIC) concentrations in groundwater were consistently higher (by as much as an order of magnitude) than in surface water discharges. During the summer months, groundwater flow contributes about as much nutrient load to the bay as does streamflow. During the winter, the groundwater contribution to nutrient loading is about 20% of the streamflow contribution. Our findings indicate that groundwater is a significant component of terrestrial nutrient and freshwater loading to Tomales Bay, particularly so during the summer months. However, neither groundwater nor streamflow nutrient fluxes are large in comparison to the mixing flux at the bay mouth or the flux of N₂ gas across the air-water interface.     

Groundwater contribution to the nutrient budget of Tomales Bay,California

Tomales Bay, a graben structure along the San Andreas Fault, was selected for modeling ecosystem nutrient dynamics because of its linear, one-dimensional morphology and relatively pristine state. Groundwater is a potentially important term in the nutrient budget. The geologic complexities created by the San Anreas Fault, however, complicate the hydrogeology and require the area to be subdivided into three regions: granite to the west, Franciscan Formation to the east, and alluvial fill in the trough. Nutrient concentrations in the groundwater were determined through extensive well sampling; groundwater discharge was estimated using both Darcy's Law calculations and a soil moisture budget. Results indicate that groundwater discharge is of the same order of magnitude as summer streamflow into the Bay, while being significantly less than other freshwater inputs in winter. Dissolved nutrient (phosphate, nitrate + nitrite, ammonium, silica and DIC) concentrations in groundwater were consistently higher (by as much as an order of magnitude) than in surface water discharges. During the summer months, groundwater flow contributes about as much nutrient load to the bay as does streamflow. During the winter, the groundwater contribution to nutrient loading is about 20% of the streamflow contribution. Our findings indicate that groundwater is a significant component of terrestrial nutrient and freshwater loading to Tomales Bay, particularly so during the summer months. However, neither groundwater nor streamflow nutrient fluxes are large in comparison to the mixing flux at the bay mouth or the flux of N₂ gas across the air-water interface.     

下辽河平原农业生态系统不同施肥制度的土壤养分收支

本试验是在潮棕壤上进行了10年的定位试验,研究了在养分循环再利用的基础上采取不同施肥制度下作物养分移出量,并结合施肥量计算出土壤中N,P,K养分收支。结果表明,在保持农业系统养分循环再利用的基础上,根据养分供给力设计化肥施用量,不仅可实现作物主产,而且可平衡土壤养分收支,避免土壤中肥料养分过剩（主要是N）进入环境,并揭示了我国我国在20世纪70年代以前大面积农田土壤缺P和80年代农田土壤大面积缺K的原因。     

The nutrient budget of a small eutrophic loch and the effectiveness of straw bales in controlling algal blooms

1. A 1-year intensive study of nutrient flows in Airthrey Loch, central Scotland, a small eutrophic [mean total phosphorus (TP) = 61.1 μg P l^–1] well-flushed freshwater body (area, 6.9 ha; mean depth, 1.85 m; volume, 1.274 × 10⁵ m³; retention time, 0.44 yr), was undertaken.
2. The nutrient budget was dominated by large allochthonous P inputs, equivalent to an areal load to the loch of 8.56 kg P ha^–1 yr^–1, which occurred predominantly during winter. In the summer, when TP inputs were low, water column levels of TP still increased, as a result of aerobic P release from sediments.
3. Sorption experiments indicated potential for sediment P release at water P concentrations of up to 200 μg P l^–1.
4. Aerobic release rate of P from sediments to the water column of Airthrey Loch was estimated to be of the order of 1 mg P m^–2 day^–1, and occurred during periods of elevated water column pH.
5. Straw bales placed in the loch to retard algal blooms were found not to have any demonstrable impact on algal concentrations observed during the study.     

Estimation of the long-term nutrient budget and thresholds of regime shift for a large shallow lake in China

In this study, we apply an integrated empirical and mechanism approach to estimate a comprehensive long-term (1953–2012) total nitrogen (TN) and total phosphorus (TP) loading budget for the eutrophic Lake Chaohu in China. This budget is subsequently validated, firstly, by comparing with the available measured data in several years, and secondly, by model simulations for long-term nutrient dynamics using both Vollenweider (VW) model and dynamic nonlinear (DyN) model. Results show that the estimated nutrient budget is applicable for further evaluations. Surprisingly, nutrient loading from non-point sources (85% for TN and 77% for TP on average) is higher than expectation, suggesting the importance of nutrient flux from the soil in the basin. In addition, DyN model performs relatively better than VW model, which is attributed to both the additional sediment recycling process and the parameters adjusted by the Bayesian-based Markov Chain Monte Carlo (MCMC) method. DyN model further shows that the TP loading thresholds from the clear to turbid state (631.8 ± 290.16 t y⁻¹) and from the turbid to clear state (546.0 ± 319.80 t y⁻¹) are significantly different (p < 0.01). Nevertheless, the uncertainty ranges of the thresholds are largely overlapped, which is consistent with the results that the eutrophication of Lake Chaohu is more likely to be reversible (74.12%) than hysteretic (25.53%). The ecosystem of Lake Chaohu shifted from the clear to turbid state during late 1970s. For managers, approximately two-thirds of the current TP loading must be reduced for a shift back with substantial improvement in water quality. Because in practice the reduction of loading from a non-point source is very difficult and costly, additional methods beyond nutrient reduction, such as water level regulation, should be considered for the lake restoration.     

The nutrient budget of a small eutrophic loch and the effectiveness of straw bales in controlling algal blooms

1. A 1-year intensive study of nutrient flows in Airthrey Loch, central Scotland, a small eutrophic [mean total phosphorus (TP) = 61.1 μg P l^–1] well-flushed freshwater body (area, 6.9 ha; mean depth, 1.85 m; volume, 1.274 × 10⁵ m³; retention time, 0.44 yr), was undertaken.
2. The nutrient budget was dominated by large allochthonous P inputs, equivalent to an areal load to the loch of 8.56 kg P ha^–1 yr^–1, which occurred predominantly during winter. In the summer, when TP inputs were low, water column levels of TP still increased, as a result of aerobic P release from sediments.
3. Sorption experiments indicated potential for sediment P release at water P concentrations of up to 200 μg P l^–1.
4. Aerobic release rate of P from sediments to the water column of Airthrey Loch was estimated to be of the order of 1 mg P m^–2 day^–1, and occurred during periods of elevated water column pH.
5. Straw bales placed in the loch to retard algal blooms were found not to have any demonstrable impact on algal concentrations observed during the study.     

Phosphorus speciation in Myall Lake sediment, NSW, Australia

The amount of phosphorus and its fractions in the sediment of Lake Myall, NSW, Australia, was assessed using a sequential extraction technique. Five sedimentary phosphorus reservoirs were measured, namely loosely sorbed phosphorus (NH₄Cl–P), iron associated phosphorus (BD–P), calcium bound phosphorus (HCl–P), metal oxide bound phosphorus (NaOH–P) and residual phosphorus (organic and refractory P, Res-P). Samples were taken from the deep and shallow sites of the lake. During the analysis, the average concentrations of each fraction of phosphorus was calculated. The results depicted that the total phosphorus (TP) content and chemically extractable phosphorus in both fine and coarse sediment fractions from the deep sites of the lake were significantly higher than those of the shallow sites, except for HCl–P extracted from the fine sediment fraction. Sediment TP was also strongly and positively correlated to sediment Fe. The phosphorus in the sediment mainly consisted of BD–P and Res-P, while NH₄Cl–P and HCl–P only contributed a minor part. The rank order of the different phosphorus extracts was similar for the two sites, namely Residual-P > BD–P > NaOH–P > HCl–P > NH₄Cl–P.     

Groundwater influence on the water balance and nutrient budget of a small natural wetland in Northeastern Victoria,Australia

Despite the critical role of water movement in the nutrient dynamics of wetlands, few wetland studies of nutrient imports, exports and cycling have been based on comprehensive water balance studies. In particular, many investigations have underestimated the importance and role of groundwater movement. Nutrient loads entering and leaving a 2 ha reed swamp in the Kiewa Valley, North-east Victoria showed the swamp to be a nutrient source within the landscape under both base flow and storm flow conditions. During a dry period between February 1994 and January 1995 the wetland itself exported 230 kg of Total Nitrogen (115 kg ha⁻¹ yr⁻¹) and 24 kg of Total Phosphorus (12 kg⁻¹ ha⁻¹ yr⁻¹). Investigations confirmed that the wetland was a significant discharge area, and that groundwater accounted for 97% of the surface water and 50% of the Total Nitrogen and Total Phosphorus load leaving the system. A further 30% of Total Nitrogen and 26% of Total Phosphorus leaving the wetland was not attributable to rain/dust, surface water inputs or groundwater, and most likely resulted from the flushing of previously stored nitrogen and phosphorus. A fire which burnt most of the wetland area in September 1994 had little immediate impact on nutrient loads leaving the system. The study illustrates the complexity of assessing the nutrient dynamics and hydrology of natural wetlands, and raises questions with respect to the use of such systems for the interception of diffuse source nutrient loads within rural catchments.     

Sediment microbial enzyme activity as an indicator of nutrient limitation in Great Lakes coastal wetlands

1. We compared the extracellular enzyme activity (EEA) of sediment microbial assemblages with sediment and water chemistry, gradients in agricultural nutrient loading (derived from principal component analyses), atmospheric deposition and hydrological turnover time in coastal wetlands of the Laurentian Great Lakes. 2. There were distinct increases in nutrient concentrations in the water and in atmospheric N deposition along the gradient from Lake Superior to Lake Ontario, but few differences between lakes in sediment carbon (C), nitrogen (N) or phosphorus (P). Wetland water and sediment chemistry were correlated with the agricultural stress gradient, hydrological turnover time and atmospheric deposition. 3. The N : P ratio of wetland waters and sediments indicated that these coastal wetlands were N‐limited. Nutrient stoichiometry was correlated with the agricultural stress gradient, hydrological turnover time and atmospheric deposition. 4. Extracellular enzyme activity was correlated with wetland sediment and water chemistry and stoichiometry, atmospheric N deposition, the agricultural stress gradient and the hydrological turnover time. The ratios of glycosidases to peptidases and phosphatases yielded estimates of nutrient limitation that agreed with those based solely on nutrient chemistry. 5. This study, the first to link microbial enzyme activities to regional‐scale anthropogenic stressors, suggests that quantities and ratios of microbial enzymes are directly related to the concentrations and ratios of limiting nutrients, and may be sensitive indicators of nutrient dynamics in wetland ecosystems, but further work is needed to elucidate these relationships.     

Short-term impacts of Phragmites management on nutrient budgets and plant communities in Great Lakes coastal freshwater marshes

Wetlands Ecology and Management - Invasive plant management is a key focus of wetland managers, and considerable resources have been devoted to control of non-native Phragmites australis in many...     

Physico-chemistry,destratification and nutrient budget of a lowland eutrophicated Malaysian reservoir and its limnological implications

Subang Lake (3° 10N, 101°29E) is a stratified lowland reservoir with a marked chemocline of some variables that probably contributes to a greater species diversity and vertical layering of plankton communities. Destratification occurs in the reservoir and is probably seasonal. Destratification results in toxic and deoxygenated waters as well as nutrient replenishment from the hypolimnion and could cause sudden mass fish and zooplankton mortality and consequent algal blooms. The nutrient budget study indicates that the reservoir is naturally oligotrophic with phosphate as a limiting factor and the high nutrient loading of the auxiliary water intake from a nearby river, Buloh River, is the cause of eutrophication in the reservoir.