Retracted: Study of the change of water quality for a lake in Central China

Water environment has undergone several state changes, and the factors responsible for causing these water state changes are different. In this paper, a fuzzy comprehensive-quantifying assessment (FCQA) is proposed to evaluate the water quality changes for a representative lake in central China in recent decades. The innovation assessment method develops an index, S_mid, by applying a quantifying method to the fuzzy comprehensive assessment (FCA). The water quality of the lake is evaluated, and the temporal and spatial variations are analysed based on the data of 1991–2006. The Gray Filling Model [GM (1,1)] was used to predict the water quality trends in the subsequent 5 years, and the possible factors responsible for causing water environmental changes were analysed. The temporal and spatial variations of water quality show that there is a strong relationship between human activities and the water quality, and that excessive pen fish farming is the key internal pollution source threatening the lake at present.     

Temporal variations in dissolved organic carbon concentrations in upland and lowland lakes in North Wales

Over a period of 18 months, the dissolved organic carbon (DOC) concentration of a series of four lakes in North Wales was measured monthly. The lake catchment profiles consisted of an upland thin peat/soil (Llyn Cwellyn), an upland thin peat/soil associated with an adjacent area of small bog (Llyn Teyrn), an upland blanket bog (Llyn Conwy), and large lowland fen and fertile agricultural area (Llyn Cefni). The results examine the indirect effect of temperature and precipitation on the DOC concentrations found in the lakes fed by the catchments. The lowest DOC of the four sites was observed for Llyn Teyrn, varying from 1.2 to 3.30 mg/L, and with the highest being recorded for Llyn Cefni (5.45–10.83 mg/L). Temperature and rainfall data were both collected. Correlations with the DOC exhibited significant relationships with temperature for three of the sampled lakes Cwellyn (r 0.490), Teyrn (r 0.640) and Cefni (r 0.472). Recomputation versus 30‐ and 60‐day temperature lag times improved the correlation coefficients. The data showed weak and insignificant correlations for DOC versus rainfall for the three lakes, but the upland lake, Llyn Conwy, with its blanket bog catchment, did not demonstrate any statistical correlation with temperature, although it did show a significant correlation for DOC versus rainfall (r 0.553, P < 0.05). Over the sampling period, although tentative relationships were found among temperature, rainfall and DOC levels, an indirect association tempered by site hydrology is suggested.     

Long‐term impacts from damming and water level manipulation on flow and salinity regimes in Lake Urmia,Iran

Lake Urmia in the north‐west of Iran is very large, very shallow and several times more saline than ocean water. The salinity of this terminal lake is of great ecological consequence for the existence and growth of Artemia Urmiana, a unique zooplankton endemic to the lake. It is a main food source for large bird populations. During the past decades, Lake Urmia has been strained by a number of anthropogenic and natural causes. They include extensive damming on the contributory rivers, building a dike‐type causeway and climate change. This paper deals with the long‐term impacts of damming, fresh water overexploitation and water level manipulation on flow and salinity conditions in Lake Urmia. For this purpose, the flow and salinity regimes were numerically simulated for the next four decades. The validity of the pseudo‐three‐dimensional hydrodynamic and advection‐dispersion models was assessed through sensitivity analysis of the models and comparing the simulated results against field measurements. The model predicted that because of damming on the rivers, the mean water level in the lake will possibly experience a drop of 2.2–2.8 m over next 40 years. The results indicated that, over decadal time periods, the lake most probably will be split into two interconnected smaller lakes. The northern lake was foreseen to become extremely saline, which will seriously threaten the Artemia's survival in this area. Over the long‐term periods, the southern lake seemed not to deviate much from its existing conditions. It however appeared to become more responsive to seasonal climatic changes and to the rivers inflow, as compared with its current conditions. Effects from climate changes were not considered in the current study.     

Four decades of the morphological dynamics of the lakes in the Jianghan Plain using Landsat observations

Using four decades of Landsat observations between 1978 and 2014, we documented and studied the long‐term dynamics of the inundation conditions in the Jianghan Plain, Central China. Three morphological factors, including inundation areas, perimeters and shoreline developments (SDs), of the 51 selected lakes were calculated. Significant long‐term morphological changes were found in lakes in the Jianghan Plain. The total area dramatically increased from 838.0 km² in 1978 to 1200.8 km² in 1989, and an overall decreasing trend was observed in the later period. The changing patterns of the perimeters and SDs were different from the inundation areas, especially for the largest lake in this area (Honghu). The inconsistent changes between the inundation area and the other two morphological parameters were likely caused by increasing human activities. This study demonstrated the importance of remote sensing in obtaining multi‐decadal lake changes in terms of both the inundation area and the morphological complexity.     

An improved technique for estimating mean depth of lakes

We describe a technique for determining mean lake depth utilizing a systematically aligned dot grid. This technique is, on average, 55% faster than the traditional planimeter methods, depending on the type of planimeter and the size and complexity of the lake. No detectable bias is associated with results from this technique compared with those of traditional planimeter methods. The relationship N_D = ⁴√A; where N_D = the number of dots falling within the shoreline of the lake and A = the surface area of the lake in ft², gives a quick estimation of the number of dots that should fall within the shoreline boundary of a lake for optimum sampling.     

Controlling harmful cyanobacterial blooms in a hyper-eutrophic lake (Lake Taihu, China): the need for a dual nutrient (N & P) management strategy

Harmful cyanobacterial blooms, reflecting advanced eutrophication, are spreading globally and threaten the sustainability of freshwater ecosystems. Increasingly, non-nitrogen (N₂)-fixing cyanobacteria (e.g., Microcystis) dominate such blooms, indicating that both excessive nitrogen (N) and phosphorus (P) loads may be responsible for their proliferation. Traditionally, watershed nutrient management efforts to control these blooms have focused on reducing P inputs. However, N loading has increased dramatically in many watersheds, promoting blooms of non-N₂ fixers, and altering lake nutrient budgets and cycling characteristics. We examined this proliferating water quality problem in Lake Taihu, China’s 3rd largest freshwater lake. This shallow, hyper-eutrophic lake has changed from bloom-free to bloom-plagued conditions over the past 3 decades. Toxic Microcystis spp. blooms threaten the use of the lake for drinking water, fisheries and recreational purposes. Nutrient addition bioassays indicated that the lake shifts from P limitation in winter-spring to N limitation in cyanobacteria-dominated summer and fall months. Combined N and P additions led to maximum stimulation of growth. Despite summer N limitation and P availability, non-N₂ fixing blooms prevailed. Nitrogen cycling studies, combined with N input estimates, indicate that Microcystis thrives on both newly supplied and previously-loaded N sources to maintain its dominance. Denitrification did not relieve the lake of excessive N inputs. Results point to the need to reduce both N and P inputs for long-term eutrophication and cyanobacterial bloom control in this hyper-eutrophic system.     

Die umweltfaktoren, die die verbreitung und entwicklung von Chalcalburnus tarichi (PALL. 1881) (Pisces: Cyprinidae) in Burdur-See begrenzen

Burdur Lake, an entirely closed and brackish water lake, having an area of 190 km² and 76 m depth, is located in the “Lakes Region” of Anatolia, 4 km from the west of Burdur city.There have been made many attempts to breed an economically important fish population but all attempts were unsuccessful. During 1946–1948 some hydrobiological investigations were carried out. According to these investigations, hydrobiological conditions of the lake were found to be suitable for Chalcalburnus tarichi (PALL. 1881) (Pisces: Cyprinidae), a fish which is endemic to the Lake Van in eastern Anatolia. Since 1966 an attempt has been made to breed Chalcalburnus tarichi artificially. This attempt was successful, but the economic productivity was not in the estimated level. These fish live in all the depth of the lake, but during the breeding season, they go into fresh water streams flowing into the lake.To find out the reasons of the productivity losses, new hydrobiological investigations have been going on since 1969. Two research stations have been chosen (Fig. 1), where water, plankton and bottom samplings have been collected for hydrobiological research. Nansen bottles were used to take the water samples, in 10 m intervals, from the surface of water towards the bottom. The chemical analysis of water have been done according to the standard methods given in Welcher (1963). The Winkler method is used to find out the amount of dissolved oxygen (Welcher, 1963).Plankton was collected in 10 m intervals by usual type Closing net (20 cm dia, mesh size of 0.05 mm). The amount of plankton per m³ has been calculated according to the Settling methods of Welch (1948).Bottom samples were collected by Ekman's Dredge at four different regions marked (a), (b), (c), (d), on Fig. 1. Samples were wet sieved through four graded sieves (mesh sizes 0.5–2.0 mm). The number of the collected bottom animals per m² were calculated.Observations showed that, the direct flow of waste waters having organic materials from the Burdur Sugar Mill, Milk-Cheese factories and Attar of Rose industries and Hemp (Cannabis sativa) maceration remnants go to the bottom of the lake, therefore, unoxygenated and thereby a hydrogensulphonized water layer is formed by the above mentioned waste products. The unoxygenated water layer level increases 2–2.5 m per year towards the surface. This pollution has caused this unexpected loss of productivity of fish, for this water layer harms the bottom feeding and planktonic organisms and restricts the spreading and development of the adopted Chalcalburnus tarichi (PALL. 1881). It is also clear that this situation is a threat to the future of the lake and its environment.     

Measuring Urban Design: Metrics for Livable Places,by Reid Ewing and Otto Clemente

In this article I examine the relationship between post-industrial growth and planning in three great cities: New York, Paris, and London. Each has taken a different approach to its post-industrial transformation. New York's approach, the Manhattan strategy of intensive development, emphasizes growth in and around the central business district. The Parisian approach, the axes strategy of extensive development, spreads growth through the larger region. London's approach, containment by zoning, stresses a balance between commercial growth and the preservation of neighborhoods and green space. I analyze each strategy as a product of a city's governmental structure, its control over local markets, and its developmental conditions. Each strategy reflects the historic practices of its respective city and entails its own costs and benefits.     

Interstate spillovers of private capital and public spending

The analysis estimates the economic returns on public spending by transportation and non-transportation functions vs. private capital, using a panel data set for 48 contiguous states from 1989 through 2002. These actual spending dollars are used as a more precise measure compared to apportioned state public capitals used in the existing literature. For each type of capital/spending, the interstate spillovers were constructed in such a way that different states are weighted by commodity flows across the states to reflect different degree of inter-state dependence. We find that when spending data rather than capital stock is used, all of the interstate spillover effects are negative and statistically significant, suggesting that infrastructure investment does not contribute to economic growth (at least not directly). Therefore, crowding out effects exist among states competing for both private and government funds, in particular if states are highly dependent on allocation of federal funds. These results confirm the finding that previously estimated positive coefficients reflect spurious correlation based on capital stocks and output.     

Features of the elemental composition of plants of northern Western Siberian palsas

This paper reports the current state of lake and wetland ecosystems in the north of Western Siberia and describes the mechanisms of their formation and succession. Elemental composition of lake water and macrophytes of the four most typical subarctic lake ecosystems in Western Siberia were analysed using ICP MS. We selected the species of Menyanthes trifoliata L. as an example of the biogeochemical system. The general dynamics of concentration of the chemical elements in M. trifoliata L. in all four ecosystems demonstrate the minimal concentrations of rare-earth elements, of which the mobility in fresh waters and the bioavailability are low. Similar properties are exhibited by all tri and tetravalent hydrolysates. We also calculated, at each of the four stages of development of the lake ecosystems, the coefficients of biological accumulation of chemical elements by M. trifoliata L. (Kb) relative to the water. This revealed that the M. trifoliata L. strongly accumulates heavy metals, such as Pb, Zn, Sr and Co. The sources may be both global factors (atmospheric transport, water treatment, etc.) and various types of local pollution occurring as a result of anthropogenic impact on ecosystems of the north.     

Surface runoff estimation over heterogeneous foothills of Aravalli mountain using medium resolution remote sensing rainfall data with soil conservation system‐curve number method: A case of semi‐arid ungauged Manesar Nala watershed

Manesar Nala watershed, having an aerial extent of 71.53 km², was subjected to modelling of its hydrological behaviour for assessing its water resource potential. Modern tools and techniques of Remote Sensing (RS) and Geographic Information System (GIS) were used for assessment of runoff generating potential using the Hydrologic Soil Cover Complex (HSCC) Method [U.S. Department of Agriculture (USDA)‐Soil Conservation System‐Curve Number (SCS‐CN) approach]. RS and GIS were used in generation and integration of thematic maps [such as Land use/Land cover (using LISS‐III data) and Hydrologic Soil Group (HSG), (using soil map of study area) to derive the Curve Number (CN) for simulating Runoff (R_o)]. The daily rainfall (P) data for the study period 2002–2015 were acquired from NOAA Climate Prediction Center (NCPC). Corresponding R_o from the watershed for intense storm events for 14 years were calculated through RS and GIS. GIS and SCS‐CN model was employed for modelling the runoff production to study its hydrological behaviour. The study showed that the Manesar Nala watershed was having a composite Curve Number – II (CN_II) value of 82.5 for normal conditions. For dry and wet conditions these values were estimated at 66.44 (CN_I) and 91.56 (CN_III), respectively. This investigation showed that Manesar Nala watershed exhibited an annual average (of 14 years, 2002–2015) R_o volume of 4 542 514.37 m³ based on the average annual rainfall (P) of 0.72 m (720 mm). The average annual surface runoff (R_o) was predicted to be approximately 0.21 m with annual runoff coefficient (C_R) of 0.29. During the study, we also found a strong correlation ‘r’ between satellite driven P and R_o from NRCS‐CN method of the order of 0.94. The methodology so developed has the potential to be used in other similar ungauged watersheds in the same agro‐climatic conditions for the purpose of planning of watershed conservation measures and other developmental activities.     

Bioassays and the algal populations of Hastings Lake, Alberta, Canada

During summer 1978 an analysis was made of the biomass development and algal species composition of Hastings Lake, a shallow eutrophic lake near Edmonton, Alberta, Canada. The algal growth potential of Hastings Lake water during the period of investigation was of particular interest. Bioassays were carried out using untreated water, water inoculated with Anabaena flos-aquae (competition experiments) and filtered or autoclaved water.The results of bioassays with untreated Hastings Lake water were well correlated with the biomass development in the lake. Bioassays with unialgal cultures in filtered or autoclaved water were carried out to obtain information concerning the nutrient situation in the lake. Iron and/or phosphorus appear to be important limiting factors during the summer period in Hastings Lake.     

Recovery of polluted lakes. a swedish research program on the effects of advanced waste water treatment and sewage diversion

In order to elucidate the effects of the effluents from advanced wastewater treatment plants for phosphorus removal, the National Swedish Environment Protection Board during 1972 started a program for analysing the conditions in a number of different recipient lakes. This study of recovery of polluted lakes also includes some recipient lakes from which sewage effluent will be completely diverted. This paper presents the program, some new methods used and the treatment plants and recipient lakes involved. The project. including 18 lakes and 15 sewage treatment plants, is running in cooperation with 13 Provincial Governments and 16 Municipalities. The efficiency of the sewage treatment plants, is continuously monitored by a new method called Minitest, and the nutrient loadings from these plants as well as from other sources are calculated.As the water quality of many recipient lakes showed great variations during the vegetation period (see Fig. 2), a need for a frequent sampling exists in these lakes.In order to simplify the sampling procedure sampling on the shore (after pumping water from the sampling point) has been introduced. Data obtained after analysing samples taken from a boat and samples from the same area taken on the shore after pumping through a 600 m plastic tube showed good agreement (see Table 2).The lake water samples are preserved by freezing, Analyses after rapid thawing showed that this method can be used also when determining from cell material easily leaking ions such as PO₄, NO₃ etc. (see Tables 3 and 4).The sewage treatment plants, the recipient lakes and some background data are presented in Tables 5 and 6. The water quality of the lakes is illustrated with the correlation between chlorophyll A and suspended solids (Fig. 3). The correlation coefficient = + 0–88. The first sign of lake recovery has been observed after an 85 per cent reduction of the waste phosphorus load. Post-precipitation (A1-sulphate) decreased the yearly load from 2000 kg P to 300 kg, which gave a 50 per cent reduction of the P content of the recipient water. Also the chlorophyll values decreased (Table 7).The role of nitrogen and phosphorus as algal growth limiting nutrients has been studied by using an algal assay procedure. N limited the growth of Selenastrum capricornutum in of the samples. In filtered lake water P was the growth limiting nutrient at total-P values below 0–05 mg 1⁻¹. Above 0·1 mg P 1⁻¹ N played the principal role. Between these values the growth was primarily limited by P or N or chelating agents (Fig. 4).     

Effect of chelators on the suitability of natural waters for hydrilla growth

The role of chelators in affecting the suitability of natural water for growth of a submersed nuisance aquatic plant, Hydrilla verticillata, has been investigated. Screening studies were done using four synthetic chelators [ethylenedinitrilotetraacetic acid, disodium salt, Na₂ EDTA·2H₂O; ethyleneglycolbis (aminoethyl) tetraacetic acid, EGTA; 1,2-diaminocyclohexanetetra-acetic acid, disodium salt, Na₂CDTA; ethylenediamine-N,N′-diacetic acid, EDDA] and naturally occurring chelators, as a peat extract and as a water sample from Lake Starvation. Analyses included dissolved oxygen and inorganic and organic carbon measurements, as well as nutrient concentrations (calcium, magnesium). The growth characteristic, defined as the per cent dissolved oxygen increase in the presence of hydrilla, was found to be associated with the amount of iron present. For EDTA and CDTA, this quantity also showed a positive relationship with k_o2, the first pseudo first-order rate constant for oxygen production, as expected. This was not seen in the case of EGTA, and this anomaly is attributed to the stable chelation of calcium by EGTA. The availability of calcium ion and, therefore also, the availability of inorganic carbon with which calcium is known to form ion-pair complexes, play a role in making a medium suitable for hydrilla growth. The behavior of natural chelators is complicated, but they could act as iron-transport agents or as calcium-sequestering agents, and their presence in a lake may alter the suitability of the lake for hydrilla growth. The limitations and significance of these points with reference to potential control of hydrilla, are presented and discussed.     

Aeration as a tool to improve water quality and reduce the growth of hydrilla

Aeration of artificial, model lake systems was studied as a tool to improve water quality and to control the growth of a nuisance aquatic weed, Hydrilla verticillata (L.F.) Royle, which has been recognized as a plant pest since the mid-1960s. Aeration decreased the growth of Hydrilla by 20% fresh weight and 18% dry weight on average after 21 days. The effect was due to the oxygenation of the water and not the mechanical effect of the bubbles, as verified by studies using pure nitrogen. Aeration also affected water quality. Inorganic carbon decreased; nitrate-nitrite-nitrogen decreased, more slowly in test systems than in control systems; dissolved oxygen increased to saturation within 24 h and pH increased 0.5–1.5 unit over the period of study. Phosphate-phosphorus concentration was unaffected. The concentrations of zinc, calcium and iron decreased as well. The effect of aeration upon Hydrilla growth appears to be correlated with a decrease of iron. After 7 days, iron concentrations decreased to less than 20 ppb. Iron toxicity is proposed as the mechanism responsible for creating a limiting condition for Hydrilla growth.     

Epipelic algal communities in a eutrophic northern lake contaminated with mine wastes

The effects of contaminated bottom sediments on the species composition, growth cycles and diversity of epipelic algal communities were determined between April and November 1978 in a shallow, eutrophic lake (Thompson Lake) situated in the Canadian subarctic. The sediments had become contaminated by gold mining wastes, deposited in the lake between 1941 and 1949. Although the concentrations of total mercury, copper, lead and zinc were high near the mine, averaging 440 μg kg⁻¹, and 85, 30 and 115 mg kg⁻¹, respectively, they decreased rapidly beyond this distance and were near background levels 2.1–3.0 km from the mine. The algal communities in the zone of heaviest contamination consisted of 63 species, the most common of which were Anomoeoneis vitrea, Pinnularia brebissonii and Cymbella species. There were more taxa (111–132) at stations situated 1.1–3.0 km from the mine and the main species included several forms of Achnanthes, Fragilaria and Navicula. Although epipelic densities in the zone of heaviest contamination were only about 50% of those recorded at the other stations, the seasonal growth patterns of the flora were generally similar throughout the lake. Based on these data, it is concluded that: (1) Mine wastes may have a long-term impact on epipelic algae in northern environments; (2) The effects of heavy metal pollution on the epipelon in subarctic lakes are similar to those in temperate zone systems; and (3) No species or group of species could be designated as indicators of heavy metal contamination.     

2000—2018年坝上高原湿地遥感动态监测与生态环境变迁

坝上高原湿地的存在对于维护京津地区的生态安全,促进区域发展具有十分重要的作用,坝上高原属典型的气候过渡区与农牧交错区,生态环境极其脆弱,随着社会经济的持续发展和人口数量的不断增加,越来越多的因素威胁着坝上高原湿地的安全而导致其生态环境的变迁。本文获取坝上高原2000年(ETM+)、2010年(TM)、2018年(Landsat 8 OLI)3期遥感影像数据,进行湿地信息提取,结果表明:2000—2018年,研究区湿地面积从796.90 km²减少至666.24 km²,湿地资源斑块数从731块减少至316块,18年间,湿地资源面积减少速度为7.26 km²/a；从湿地类型变化来看,主要是湖泊湿地面积的减少,减少106.2 km²,斑块数减少242块,湖泊湿地面积的减少在2010—2018年阶段速度较快,减少速度为8.70 km²/a；从湿地资源变化空间分布来看,坝上高原西部萎缩趋势整体高于东部,坝上高原湿地面积的减少主要体现在西北内流区,西北内流区湿地面积减少97.86 km²,占整个坝上高原湿地减少面积的74.90%,斑块数减少366块,占整个坝上高原湿地斑块减少数量的88.19%。     

Growth and nutrient uptake of green alga, Scenedesmus dimorphus, under a wide range of nitrogen/phosphorus ratio—I. Experimental study

In order to elucidate the relation between algal growth and nutrients such as nitrogen and phosphorus, a chemostat culture experiment using Scenedesmus dimorphus was performed under the conditions of T-N/T-P ratio of 2–50 mg N mg⁻¹ P and dilution rate of 1–4 day⁻¹. It was ensured from the results that nitrogen and/or phosphorus is the limiting nutrient for the growth of this alga under these conditions. The optimum T-N/T-P ratio for its growth was observed to change from 20 to 5 mg N mg⁻¹ P as the dilution rate varied from 1 to 4 day⁻¹ and, in most of the range of T-N/T-P ratio and dilution rate, its growth rate was not regulated by only one of the available nitrogen and phosphorus concentrations in the medium and algal nitrogen and phosphorus contents. Based on these facts, the multiplicative effect rather than the threshold effect of these two nutrients on its growth was considered to exist. It has been suggested, however, that algal nitrogen and phosphorus contents, especially nitrogen content, are the most important factors regulating its growth. Nitrogen uptake rate of this alga increased at a given concentration of available nitrogen in the medium as T-N/T-P ratio decreased down to 2 or 5 mg N mg⁻¹ P. It is also suggested that a multiplicative effect of nitrogen and phosphorus on uptake of these nutrients by S. dimorphus may exist.     

Growth of organic films on indoor surfaces

We present a model for the growth of organic films on impermeable indoor surfaces. The model couples transport through a gas‐side boundary layer adjacent to the surface with equilibrium partitioning of semivolatile organic compounds (SVOCs) between the gas phase and the surface film. Model predictions indicate that film growth would primarily be influenced by the gas‐phase concentration of SVOCs with octanol‐air partitioning (K_oa) values in the approximate range 10≤log K_oa≤13. Within the relevant range, SVOCs with lower values will equilibrate with the surface film more rapidly. Over time, the film becomes relatively enriched in species with higher log K_oa values, while the proportion of gas‐phase SVOCs not in equilibrium with the film decreases. Given stable airborne SVOC concentrations, films grow at faster rates initially and then subsequently diminish to an almost steady growth rate. Once an SVOC is equilibrated with the film, its mass per unit film volume remains constant, while its mass per unit area increases in proportion to overall film thickness. The predictions of the conceptual model and its mathematical embodiment are generally consistent with results reported in the peer‐reviewed literature.     

Effects of artificially introduced ground water on the chemical and biochemical characteristics of six Hillsborough County (Florida) lakes

Six lakes in Northwest Hillsborough County, Florida, were sampled synoptically and the water samples were analyzed for selected chemical and biochemical characteristics. The lakes are closely grouped geographically and had four different histories of being pumped. i.e., having water from a deep aquifer pumped into the lake to maintain levels. The histories included two lakes that had never been pumped, two that had been recently pumped, one that had been pumped sporadically and one that had been continuously pumped for several years. Chemical analyses of the water samples included: pH, dissolved oxygen, carbon (inorganic and organic), calcium, hardness, major macronutrients (orthophosphate, nitrate and nitrite nitrogen), tannic acid, color and total iron. Two of the lakes are infested with hydrilla (Hydrilla verticillata Royle), and a biochemical characteristic was measured: the rate of growth of hydrilla in the various water samples. The growth characteristic was defined as the per cent dissolved oxygen increase in the presence of hydrilla under defined conditions. Analysis of the data suggest that the lakes can be divided into two groups based upon the growth characteristic and water hardness: those that have never been pumped and those that have been pumped. The first had comparatively low values for hardness (30 ppm) and growth characteristic (19 ± 1% increase in dissolved oxygen); the second group had significantly higher values of 68 ± 5 ppm and 74 ± 6% for the hardness and growth characteristic, respectively, the significance and limitations of these observations are discussed, particularly in reference to the potential for hydrilla proliferation.