Assessment of River Water Quality in Northwestern Greece

The effect of land use patterns on river water quality was studied in three different river basins located in Epirus, Northwestern Greece. Studies were conducted from October 2000 to {September} 2001. During this period, the parameters chemical oxygen demand (COD), biological oxygen demand (BOD), NO_2–, NO_3–, NH₄₊ and PO_43– were measured, employing standard methods of analysis. The results were subjected to principal component analysis (PCA) for the estimation of the underlying variable correlations and were further explored by means of cluster analysis. The values of the above parameters were also compared with those awkward in the Fresh Water Fisheries Directive (78/659/EEC). It was found that the phosphate content was much higher than the upper limiting criteria for eutrophication for salmonid waters, whereas nitrate levels were lower than the permissible criteria according to the Nitrates Directive 91/676/EEC for drinking water. The inorganic nutrient load was mostly attributed to sites that drain agricultural areas, especially during winter and spring. The organic matter was due to urban activities during autumn.     

Anthropogenic‐induced shifts in salinity and nutrient status of two freshwater tropical lakes in India

An understanding of ongoing changes in salinity and nutrient status, as influenced by anthropogenic forcing factors, is important for integrated lake basin management (ILBM) and conservation of water resources in dry tropical regions. This study analysed a range of water quality attributes, including salinity, nitrate (NO₃^?), ammonia (NH₄ ⁺ ), phosphate (PO₄ ^{3 ?}) and dissolved organic carbon (DOC) in two freshwater lakes in Rajasthan, India for three consecutive years (2000–2002). Between‐lake comparisons indicated marked differences in most of the water quality variables. The pH in both study lakes remained above neutral. Water hardness, salinity and concentrations of total dissolved salts (TDS), chlorides, NO₃^?, NH₄⁺, PO₃^3? and DOC were high in Lake Udaisagar, which received inputs from agricultural drainage and urban–industrial releases. The DOC in Lake Baghdara, which drains a woodland catchment, was similar to that for Lake Udaisagar, indicating the role of allochtonous inputs in the build‐up of DOC. The results of this study indicated that increasing human interferences have increased the nutrient concentrations in Lake Udaisagar. This factor, coupled with extended periods of dryness, drives these two freshwater lakes towards a high salinity. This study provides evidence of a human‐induced salinity increase and has relevance for ILBM and for the conservation of freshwater resources in dry regions.     

芦苇占优势农田溪流营养盐滞留能力分析与评估

2014年9月—2015年4月,在合肥地区二十埠河流域的某一典型农田源头溪流段,选择以Na Cl为保守示踪剂,NH4Cl和KH2PO4为添加营养盐,采用恒速连续投加的方式,开展了7次野外现场示踪试验。在此基础上,利用OTIS模型和营养螺旋原理,从机制层面分析和评估芦苇占优势农田源头溪流氮磷营养盐滞留能力和滞留特征。结果表明,该芦苇占优势渠段的比值As/A明显超过一般源头溪流水体,暂态存储对于营养盐滞留有较大影响;NH4+和SRP的暂态存储区营养盐一阶吸收系数都较主流区高一个数量级,且所有吸收系数均为正值,表明芦苇占优势渠段具有氮、磷"汇"的功能;NH4+吸收长度明显低于SRP,特别是冬季和初春,意味着溪流对于NH4+的滞留能力超过SRP;NH4+和SRP的总滞留率分别为14.46%和10.73%,生物滞留率平均值分别为9.17%和3.67%;主流区流动水体和暂态存储区对于NH4+滞留的平均贡献率分别为43.12%、56.88%;对于SRP滞留的平均贡献率分别50.13%、49.87%。     

Effect of Thermal Stratification on Phytoplankton and Nutrient Dynamics in a Regulated River (Saar,Germany)

The weir pool Serrig is the deepest one along the impounded river Saar. Damming caused massive changes in the river's hydrodynamics. We analyzed the spatio‐temporal variability of thermal density stratification in the weir pool and its effect on phytoplankton and nutrient dynamics. In the analysis, continuous measurements from the years 2014 and 2015 were combined with three two‐day sampling campaigns in spring 2015. Thermal stratification occurred regularly in the downstream section of the weir pool during spring and summer and showed a diurnal rhythm. Temperature differences >1 K between the 1 and 2 m water layer were observed during 34 out of 217 days (16%) in 2014, with maximum temperature gradients up to 3.71 K. Whereas the influence of thermal stratification on phytoplankton biomass and distribution was low during the algal bloom in early spring, stratification events between May and July promoted temporary algal blooms in the surface layer with chlorophyll a concentrations up to 98 µg Chla l^?1 and a maximum difference between the 1 and 2 m water layer of 36 µg Chla l^?1. Some of the stratification events resulted in reduced concentrations of dissolved nutrients in the surface layer as a result of increased uptake by algae, with maximum gradients between the surface and the 8 m water layer of 0.070 mg ortho‐PO₄^3‐‐P l^?1, 0.136 mg NH₄⁺?N l^?1 and 0.24 mg NO₃¯?N l^?1. These vertical gradients should be considered in sampling protocols for the assessment of the water quality of temporarily stratified river sections. Copyright © 2016 John Wiley & Sons, Ltd.     

Periphyton contribution to nitrogen dynamics in the discharge from a wastewater treatment plant

To evaluate the importance of periphyton to nitrogen dynamics in the discharge from wastewater treatment plants (WWTPs), we examined changes in total and inorganic nitrogen content downstream from a WWTP on the Kurose River in Hiroshima Prefecture, Japan. At 0.7 km downstream of the WWTP (point A), NH₄⁺?N was the dominant form of inorganic nitrogen, but concentrations decreased rapidly to 5 km downstream (point B). In contrast, no significant change in the [NO₂^?+ + NO₃^?]?N concentration was observed between the two points. Total nitrogen (TN) load decreased significantly between the two points, suggesting that sorption and/or denitrification occurred in the river channel. Potential rates of nitrogen sorption and transformation by periphyton were determined in a loboratory experiment in which changes in the nitrogen content of river water were examined in an acrylic chamber with periphyton. Nitrification and nitrogen removal occurred mainly in the periphyton. The contributions of periphyton activity to TN and NH₄⁺?N decrease in the field, as estimated from the results of the laboratory experiments, were 6–18% and 23–72%, respectively. These results suggest that periphyton plays an important role in decreasing NH₄⁺?N concentration in the discharge from wastewater treatment plants.     

多级拦水堰坝调控农田溪流营养盐滞留能力的仿真模拟

为揭示多级拦水堰坝对于低等级小河流营养盐滞留能力的影响,以巢湖流域某一典型的农田源头溪流为对象,在野外示踪实验和计算机模拟的基础上,针对构建的多级简易水坝,采用暂态存储和营养螺旋指标,仿真模拟多级拦水堰坝对于氮磷营养盐滞留能力的调控效果。结果表明:多级拦水堰坝Darcy-Weisbach阻力系数明显超过无堰坝情形,但其弗劳德数Fr和雷诺数Re则较无堰坝情景低些;多级拦水堰坝相应的交换长度Ls值较无堰坝情景低1~2个数量级,水力持留因子Rh则较无堰坝情景明显增大,表明多级拦水堰坝使溪流的暂态存储能力得到很大提升;在多级拦水堰坝情景下,NH4+和PO43-的吸收长度Sw均有大幅度的下降,其中NH4+削减幅度达70.27%~89.47%,PO43-为75.59%~81.92%;不仅如此,在多级堰坝情景下,NH4+和PO43-的物质传输系数Vf、吸收速率U均显著增大,表明多级拦水堰坝可以有效提高农田溪流氮磷营养盐的滞留潜力。     

Quantification of cormorant litter and nutrient deposition to Great Lakes island ecosystems

Ornithogenic nutrients derived from waterbirds such as the double-crested cormorant (Phalacrocorax auritus, Lesson) have been linked to habitat change within nesting colonies. For the islands of Lake Erie, where increasing cormorant populations and subsequent habitat change have spurred management activity, estimates of the quantity and chemical characteristics of avian-derived contributions are lacking. To evaluate the quantity and chemical characteristics of ornithogenic litterfall beneath a double-crested cormorant colony on a western Lake Erie island we investigated the mass of material and nutrient composition (PO₄^3 −, NO₃⁻ and NH₄⁺) reaching the forest floor under three nest densities (Low: 1–96 nests ha^− 1; Medium: 97–255 nests ha^− 1 and High: > 255 nests ha^− 1). As expected, litterfall (total mass) input differed among nest densities with the most substantial input (225.05 g/m² week^− 1) measured under High nest density conditions. Nutrient concentrations also showed increases with nest density to a point, where mean PO₄^3 − and NH₄⁺ concentrations showed no differences between Medium and High nest density sites. As well, NO₃⁻ concentrations were highest under Medium density, with no differences in this nutrient observed between Low and High density. Collectively, litterfall nutrient composition was similar to those linked to habitat changes in other waterbird colonies. Similarities in the concentrations of several nutrients between Medium and High nest density categories suggest that management actions aimed at reducing allochthonous nutrient contributions should try to sustain nest density at or below 96 nests ha^− 1.     

Storm effects on nitrogen flux and longitudinal variability in a river–reservoir system

Sustainable management of the nitrogen (N) cycle remains a considerable global challenge that has major implications for aquatic ecosystems. Dams play a critical yet often neglected role in addressing this challenge as they increase hydraulic residence time and denitrification potential. However, during storm events when the majority of N loading occurs, less is known about the effects dams have on N fate and transport processes. Here, we examined the flux of N species and phosphorus (P) and longitudinal profiles of nitrate (NO₃^?) along a sixth‐order river–reservoir system at baseflow and across the falling limb of a multiday, 1‐year storm hydrograph. During the storm event, the reservoir reduced total NO₃^? flux by 19.1% and P flux by 12.7%. On the contrary, ammonium (NH₄⁺) fluxes were 200% higher downstream of the dam in comparison with fluxes into the reservoir, indicating that there was a substantial net export of NH₄⁺ from the reservoir during the storm event. Longitudinally along the river to reservoir transition, a breakpoint of statistical significance was identified, highlighting the sharp contrast between NO₃^? concentrations within the river and reservoir. Results suggest that frequent storm events such as the one presented here can greatly alter N removal processes in river–reservoir systems. Overall, this study highlights the need to better understand the role that storm events play in river–reservoir N cycling dynamics.     

苏南运河对太湖主要入湖河流污染物通量的贡献率

为了解苏南运河对太湖主要入湖河流污染物通量的贡献,基于一维平原河网水量、水质数学模型,模拟计算了2011年受苏南运河影响的主要入湖河流的入湖污染物通量(COD、氨氮、TN、TP),量化分析了苏南运河对主要入湖河流入湖污染物通量的贡献率。研究结果表明:苏南运河主要影响湖西区的太湖主要入湖河流,对湖西区主要入湖河流入湖通量的总体贡献率约为23%,其中对太滆运河的贡献率最大,约42%,漕桥河次之,约23%,对太滆南运河、社渎港、陈东港污染物通量的贡献率由北向南依次减小。     

重庆老龙洞岩溶地下水化学特征及影响因素

为研究老龙洞地下河出口(G3)与表层岩溶泉(G1、G2)水化学特征差异及影响因素,利用统计方法对2012年月尺度的水化学数据进行分析。结果表明:研究区地下水水化学组成以Ca~(2+)、Mg~(2+)、HCO_3~-、SO_4~(2-)为主,水化学类型主要为Ca-HCO_3型;Ca~(2+)、Mg~(2+)、HCO_3~-浓度变异系数较小,主要来源于碳酸盐岩地层溶蚀,且以石灰岩溶解为主;硫酸与硝酸参与了碳酸盐岩的溶蚀,其中硫酸对碳酸盐岩溶蚀的影响更大;地下水中SO_4~(2-)、PO_4~(3-)、Na~+、K~+、Cl~-和NO_3~-浓度变异系数较大,主要受农业施肥、畜禽粪便、企业废水和生活污水等因素的影响;SO_4~(2-)、PO_4~(3-)、Na~+、K~+、Cl~-浓度表现为地下河高于表层岩溶泉,而NO_3~-浓度表现为地下河低于岩溶泉。     

改性凹凸棒土/纳米铁复合材料去除地下水NO_3~--N的研究

采用液相还原法制备改性凹凸棒土/纳米铁复合材料(简称复合材料),考察了该复合材料的稳定性及其作用下"三氮"(NO_3~--N、NH_4~+-N、NO_2~--N)的变化情况,阐明了地下水环境因素(DO、温度、光照)对复合材料去除NO_3~--N的影响。模拟地下水环境时,3种材料去除NO_3~--N的反应活性顺序为:复合材料纳米铁改性凹凸棒土,且复合材料作用下NH_4~+-N的转化率低,几乎无NO_2~--N生成。DO、温度对复合材料去除地下水NO_3~--N的影响较大;而光照和黑暗环境下,地下水中NO_3~--N的去除率及NH_4~+-N、NO_2~--N的生成量均无明显差异。研究成果旨在为NO_3~--N污染地下水工程修复提供理论依据和技术支撑。     

Experiences of nitrogen and phosphorus removal in deep-bed filters at Henriksdal sewage works in Stockholm

Deep-bed down-flow two-media filters were used in pilot plant studies with filtration of secondary settled wastewater. FeSO₄ or FeCl₃ was applied as a precipitation agent, and NaAc·3H₂O was chosen as a carbon source when denitrification was desired. The concentration of PO₄-P in the filtrate from the pilot plant study never exceeded 0.05 mg PO₄-P/l when iron salts were dosed. The curves showing the concentration of P-tot and PO₄-P in the filtrate as a function of the quotient between the dosage of iron and the concentration of PO₄-P in the influent to the filter followed approximately an exponential relationship. The total nitrogen reduction over the filter bed increased from an average of 2.3 mg (NO₃+NO₂-N/l at the beginning of each experiment to an average of 4.3 mg (NO₃+NO₂)-N/l towards the end of the lest. When only secondary settled wastewater, suspended solids, primary settled wastewater, iron salts, or sodium acetate was added, at a hydraulic load of 10 m/h, the time before clogging became 100 h, 10 h, 10 – 15 h, 20 – 40 h, and 20 – 40 h, respectively. Almost the entire pressure drop was located on the surface of the filter bed and 0.25 metre down in the expanded clay layer.     

The influence of the coastal plain on the downstream material fluxes from a small coastal mountainous river basin

Small mountainous coastal basins display steeper gradients, suggesting intensified river transport. However, there is little information about downstream trends in rivers with low discharge and material fluxes across coastal plains and its influence on land‐sea material transport. This study examined 2 years of river discharge, suspended sediment and nutrient concentrations, fluxes and yields from upstream to the upper estuary of a typical South‐east Atlantic Basin. This study provides data about the material retention capacity of the coastal plain. The results indicated that the coastal plain did not affect nutrient concentrations, but reduced turbidity, inducing chlorophyll a and consequently primary productivity in the lower river basin and upper estuary. The coastal plain attenuated the increasing downstream material fluxes, but also curbed suspended sediment and TN fluxes, across the lower river/upper estuary. In contrast, TP and PO₄^3? fluxes increased sharply across the coastal plain. This was influenced by natural and anthropogenic P inputs from soils and run‐off to the river channel. These exceeded the retention capacity of the coastal plain and result in a high export efficiency of this nutrient to the sea.     

SPATIAL RELATIONS OF TOPOGRAPHY,LITHOLOGY AND WATER QUALITY IN A LARGE RIVER FLOODPLAIN

Floodplains exert important controls on water and nutrient processing, yet spatial heterogeneities in floodplain characteristics result in variable effectiveness. In this study, we evaluated the spatial relations among topographic, lithologic and water quality features within the Cedar River floodplain located in southeastern Iowa. Floodplain topography and lithology were dominated by a series of sandy ridges and fine‐textured swales typical of a natural meandering river floodplain complex. Groundwater sampling results from 10 monitoring wells placed in representative ridge and swale environments indicated that water quality varied systematically. Beneath sand‐dominated ridges, water was aerobic and had low specific conductance, and higher concentration of NO₃–N and lower concentrations of PO₄–P and dissolved organic carbon (DOC). Groundwater beneath swales was anaerobic and typified by high specific conductance, and higher concentrations of NH₄–N, PO₄–P and DOC. We extrapolated the results from point measurements to the entire floodplain area using surface geophysics and light detection and ranging using co‐kriging to map the distribution of groundwater geochemical environments at the study site. Results are seen to provide an approach to better predict shallow groundwater quality in large river floodplains and improve our ability to manage ecosystem services in these strategic locations. Copyright © 2011 John Wiley & Sons, Ltd.     

Nitrogen and phosphorus changes and optimal drainage time of flooded paddy field based on environmental factors

While many controlled irrigation and drainage techniques have been adopted in China, the environmental effects of these techniques require further investigation. This study was conducted to examine the changes of nitrogen and phosphorus of a flooded paddy water system after fertilizer application and at each growth stage so as to obtain the optimal drainage time at each growth stage. Four treatments with different water level management methods at each growth stage were conducted under the condition of ten-day continuous flooding. Results show that the ammonia nitrogen (NH⁺₄-N ) concentration reached the peak value once the fertilizer was applied, and then decreased to a relatively low level seven to ten days later, and that the nitrate nitrogen (NO^-₃-N) concentration gradually rose to its peak value, which appeared later in subsurface water than in surface water. Continuous flooding could effectively reduce the concentrations of NH⁺₄-N, NO^-₃-N , and total phosphorus (TP) in surface water. However, the paddy water disturbance, in the process of soil surface adsorption and nitrification, caused NH⁺₄-N to be released and increased the concentrations of NH⁺₄-N and NO^-₃-N in surface water. A multi-objective controlled drainage model based on environmental factors was established in order to obtain the optimal drainage time at each growth stage and better guide the drainage practices of farmers. The optimal times for surface drainage are the fourth, sixth, fifth, and sixth days after flooding at the tillering, jointing-booting, heading-flowering, and milking stages, respectively.     

Temporal and spatial variations of runoff composition revealed by isotopic signals in Nianchu River catchment,Tibet

Understanding the hydrology of glaciated catchments is an important step in assessing the vulnerability of water resources to a changing climate. Based on multi-isotopes of water (²H, ¹⁸O and ³H) and dissolved radon (²²²Rn), the temporal and spatial variabilities of major hydrological processes along the main flow and tributaries in the Nianchu River catchment were examined and the isotopic response to climate variation was identified. Geographic variation in changes of isotopic composition that differ from other rivers in the Nianchu River catchment was apparent. Along the direction of runoff, river δ¹⁸O exhibited more depletion, which was closely related to water mixing and groundwater discharge. End-member mixing analysis using isotopic tracers suggested that annual recharge from summer rainfall and glacial meltwater maintained the surface water resources (their respective contributions rate were 65.9% and 26.5%); groundwater had a significant contribution on runoff in the dry season (about 46.6%). Summer rainfall and meltwater rapidly infiltrated through a series of faults and fissures and were, stored in underground reservoirs and released to runoff in the dry season, thereby ensuring rapid circulation and renewal of water resources (annual renewal proportion was about 40%). It was concluded that rainfall infiltration, meltwater and groundwater storage play important roles in the hydrology of this alpine-cold catchment. Similar to a general alpine-cold catchment, the stable isotopes (δ²H, δ¹⁸O) of river runoff will gradually be enriched, while groundwater reserves will increase in the Nianchu River catchment as a result of climate warming and an acceleration of glacial-melting.     

强化混凝技术对南淝河季节性污染物去除效果研究

针对南淝河河口水体夏秋季节藻类的质量浓度高,冬季NH_4~+-N质量浓度异常高的特点,研究强化混凝技术对藻类和NH_4~+-N的去除效果,并应用于南淝河现场构建的混凝沉淀系统。结果表明:混凝剂单独使用时,聚合氯化铝(poly aluminium chloride,PAC)的除藻效果最好,去除率为76%。选用除藻效果较好的阳离子聚丙烯酰胺(cationic polyacrylamide,CPAM)作为助凝剂,藻类的去除率显著增加,均达99%,但对NH_4~+-N的去除效果不佳;聚合氯化铝铁(poly aluminium ferrous chloride,PAFC)与CPAM的组合对NH_4~+-N的去除率最高,为7.54%。通过投加黏土矿物,增加NH_4~+-N的去除率。NaCl与MgCl_2联合改性的凹凸棒与CPAM联用时,对NH_4~+-N的去除率最高达85.65%。选用"PAFC+CPAM"作为南淝河旁路强化混凝系统的投药配方,现场应用时,夏秋季对藻类的去除率平均为88.64%;冬季对NH_4~+-N的去除率平均为24.49%。     

Hydrochemistry of Lake Rara: A high mountain lake in western Nepal

High altitude ecosystems have important natural ecological functions but are under increasing impacts from human activities and climate change. A detailed analysis of the water chemistry of Lake Rara, a high mountain lake in western Nepal, was carried out in October 2015 and April 2016. A total of 31 water samples were collected. Major ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄^2?, NO₃^? and Cl^?) were analysed by ion chromatography. Si and PO₄^3? were analysed following the standard protocols. Conductivity, pH, total dissolved solids (TDS), turbidity and dissolved oxygen (DO) were measured on‐site. The lake is oligotrophic characterized by low PO₄^3? concentration (0.06 ± 0.01 mg/L), high DO values (6.73 ± 0.06 and 10.89 ± 0.86 mg/L), alkaline pH (8.42 ± 0.3 and 8.32 ± 0.23) and low conductivity (189.93 ± 5.3 and 189.22 ± 5.8 μS/cm). The concentrations of the major cations were in the order of Ca²⁺ > Mg²⁺ > K⁺ > Na⁺ (during both seasons), and for anions, it was HCO₃^? > SO₄^2? > Cl^? > NO₃^? and HCO₃^? > Cl^? > NO₃^? > SO₄^2? during postmonsoon and premonsoon, respectively. One‐way ANOVA revealed significant seasonal variations (p  < 0.05) in most of the physicochemical parameters. The increased concentrations of most of the ions in the premonsoon time probably reflect long‐range transport of materials through dry deposition, whereas higher concentrations of NO₃^? and Cl^? in some sites possibly reflect the localized impacts of settlement and grazing. The lake water was classified as Ca(Mg)HCO₃. High (Ca²⁺ + Mg²⁺)/Tz⁺ ratio (0.97 in postmonsoon and 0.95 in premonsoon) and low (Na⁺ + K⁺)/Tz⁺ ratio (0.03 in postmonsoon and 0.04 in premonsoon) confirm carbonate weathering as the principal source of major ions with bedrock geology governing the water chemistry. The findings of this study build on the baseline dataset for assessing future anthropogenic influence on the lake and subsequent development for future lake management strategies.     

Nutrient Regeneration by Zooplankton in Southern Lake Huron

Rates of nutrient regeneration by zooplankton (μmol/mg dry wt/hr) in southern Lake Huron from April to August 1975 ranged from undetectable to 2.6 for total phosphorus (TP), undetectable to 0.8 for total soluble phosphorus (TSP), undetectable to 0.12 for soluble reactive phosphorus (SRP), undetectable to 0.97 for ammonia (NH₃), undetectable to 3.8 for nitrate plus nitrite (NO₃ + NO₂), and undetectable to 2.9 for silica (SiO₂). Two diel experiments were conducted. Times of highest rates of regeneration varied for the different nutrients on these dates. Using the average concentration of zooplankton in the surface waters during this study, the calculated average concentration of nutrients regenerated by zooplankton was 0.012 μmol P/L/ hr for TP, 0.0046 μmol P/L/ hr for TSP, 0.0016 μmol P/L/ hr for SRP, 0.0146 μmol N/L/ hr for NH₃, 0.043 μmol N/L/ hr for NO₃ + NO₂, and 0.058 μmol Si/L/ hr for SiO₂. The contribution of nutrient regeneration by zooplankton to the turnover time of the various nutrients in the surface waters was calculated to be 212 hr for TP, 239 hr for TSP, 69 hr for SRP, 62 hr for NH₃, 505 hr for NO₃ + NO₂, and 531 hr for SiO₂. Although the turnover time for most of these nutrients is fairly slow, the nutrient pools for SRP and NH₃ are replenished in less than 70 hr by nutrient regeneration. Zooplankton therefore appear to play a significant role in the cycling of SRP and NH₃ in southern Lake Huron.     

Summer phytoplankton nutrient limitation in Maumee Bay of Lake Erie during high-flow and low-flow years

Algal production in Maumee Bay in western Lake Erie is highly affected by inputs of nitrogen (N) and phosphorus (P) from the Maumee River, which drains predominantly agricultural lands, leading to the formation of cyanobacterial blooms. In a 3-year study, precipitation and discharge ranged from relatively low (2012) to relatively high (2011) with corresponding changes in the size of the cyanobacterial bloom. This study aimed to quantify the relation between river discharge and algal nutrient limitation in Maumee Bay. During the summer growing seasons, 20 nutrient enrichment bioassays were performed to determine which nutrient (P or N) might limit phytoplankton growth; and ambient N and P concentrations were monitored. The bioassays suggested that phytoplankton growth shifted from P-limited to N-limited during summer of the low and intermediate discharge years (2012 and 2010, respectively), whereas during the high discharge year (2011) phytoplankton were nutrient-replete before becoming N-limited. Phosphorus-replete growth during the high discharge year likely was due to high P loads from the river and dissolved P concentrations greater than 1 μmol/L. Symptoms of N-limited growth occurred during August and September in all three years and during July of 2012 when NO₃⁻ plus NH₄⁺ concentration was less than 7.29 μmol/L suggesting low or no correspondence between N-limitation and size of the cyanobacterial bloom. Occurrence of a relatively small cyanobacterial bloom in 2012 following the record-breaking bloom in 2011 suggests the possibility of fast-reversal of eutrophication in Maumee Bay if P loading from the watershed could be decreased.