Causes and Consequences of Changes in Nutrient Structure in the Jiaozhou Bay

Concentrations and ratios of nutrients in Jiaozhou Bay, China, have changed much in the past decades, with trends indicating an increase in nitrogen and a decrease in silicate. Statistical analysis has shown that the long-term variations of nutrients are associated with agricultural activities, precipitation, and anthropogenic factors. Stoichiometric calculations indicate that the nutrient structure has become more and more unbalanced. There has been almost no possibility for nitrogen limitation since the 1980s, the probability of P limitation has increased, and the probability of Si limitation has also increased markedly from the 1980s to the 1990s. As a consequence of changes in nutrient structure, a decrease in the abundance of net phytoplankton was evident, whereas total chlorophyll a levels have remained roughly unchanged at around 3.55 μg/L. Thus, it is likely that smaller species have taken the niche vacated by the larger species. Changes in phytoplankton size and species composition may ultimately lead to various functional and structural changes at the system level.     

广东大亚湾西南部海域营养盐结构的长期变化

分析了大亚湾西南部海域1982～2002年营养盐结构的长期变化。水域中溶解无机氮(DIN)的含量呈上升趋势,磷酸盐(PO₄^3-)含量从80年代初到90年代末逐年下降,2000年后有所恢复,硅酸盐(SiO₃^2-)的含量波动较大,但平均维持在20μmol·L^-1的较高水平上。各营养盐浓度比值的长期变化表现为氮磷比上升,硅氮比下降,硅磷比稳中有升。结合营养盐浓度及其比值的变化,可以认为大亚湾西南部海域中浮游植物生长的营养盐限制因子已经由过去的氮限制转变为磷限制;各营养盐的浓度及其比值在各季度的分布表明,浮游植物的生长春季和冬季受到氮限制的可能性较大,而夏季和秋季受磷限制的可能性较大;在营养盐的平面分布上,大鹏澳内DIN高于澳外水域,而PO₄^3-自1997年后低于澳外水域。     

Nutrient limitation of phytoplankton in solar salt ponds in Shark Bay,Western Australia

The aim of this research was to examine nutrient limitation of phytoplankton in solar salt ponds of varying salinity at Useless Inlet in Western Australia. These ponds use solar energy to evaporate seawater for the purpose of commercial salt production. A combination of techniques involving water column nutrient ratios, comparisons of nutrient concentrations to concentration of magnesium ions and bioassays were used in the investigation. Comparisons of changes in dissolved inorganic nitrogen to phosphorus ratios and concentrations of dissolved inorganic nutrients against changes in concentrations of the conservative cation Mg²⁺ indicated that phytoplankton biomass was potentially nitrogen limited along the entire pond salinity gradient. Nutrient addition bioassays indicated that in low salinity ponds, phytoplankton was nitrogen limited but in high salinity ponds, phosphorus limited. This may be due to isolation of phytoplankton in bioassay bottles from in situ conditions as well as to changes in phytoplankton species composition between ponds, and the variable availability of inorganic and organic nutrient sources. The differences in limiting nutrient between methods indicate that phytoplankton cells may be proximally limited by nutrients that are not theoretically limiting at the pond scale. Dissolved organic nutrients constituted a large proportion of total nutrients, with concentrations increasing through the pond sequence of increasing salinity. From the change in nutrient concentrations in bioassay bottles, sufficient dissolved organic nitrogen may be available for phytoplankton uptake in low salinity ponds, potentially alleviating the dissolved inorganic nitrogen limitation of phytoplankton biomass. 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     

Increasing nitrogen limitation during summer in the List Tidal Basin (Northern Wadden Sea)

The European Wadden Sea is characterized by high nutrient loads and turbid waters. Riverine nutrient input showed a gradual decrease since the mid 1980s. In the List Tidal Basin (Northern Wadden Sea) the frequency of low NO₃ values in summer has increased and decreasing mean annual suspended matter concentrations indicate an increasing underwater irradiance. We used an approach developed by Cloern (Aquat Ecol 33:3–16, 1999) to analyze resource limitation of nitrogen (DIN) and underwater irradiance for phytoplankton growth in the List Tidal Basin between 1985 and 2005. Comparing our results to other studies suggests that the List Tidal Basin is one of the most nitrogen sensitive areas of the European Wadden Sea. In 2005, phytoplankton growth was light limited from January to May and in November and December, co-limited by both resources in June, July and October, and nitrogen limited in August and September. Comparing phytoplankton growth limitation in the periods 1985–1991 and 1999–2005, the duration of nitrogen limitation during summer is significantly longer in the second period (2.1 ± 0.9 months) than in the first (0.7 ± 0.5). Moreover, light limitation in September and October has decreased in the second period. A decreasing phytoplankton growth during summer is in line with former studies from the List Tidal Basin, which showed that summer chlorophyll concentrations have decreased since the mid 1980s. We suggest that nowadays less food is available for higher pelagic and benthic trophic levels due an increased nitrogen limitation during summer.     

Nutrient regeneration by zooplankton: effects on nutrient limitation of phytoplankton in a eutrophic lake

We tested the hypothesis that excretion of nutrients by zooplanktoncan reduce the severity of nutrient limitation of phytoplankton,and determine whether the phytoplankton community is limitedby nitrogen or phosphorus. In situ experiments were conductedin eutrophic Lake Mendota (Wisconsin, USA) during the summerof 1988, where phytoplankton were limited by N and P, but periodsof nutrient limitation were transitory Increased zooplanktonbiomass and the consequent increased excretion of nutrientsby zooplankton reduced P limitation (as measured by specificalkaline phosphatase activity) in all experiments Excretionof nutrients also reduced N limitation (as measured by ammoniumenhancement response) in one of three experiments. In additionalexperiments in the more highly eutrophic Lake Wingra, excretionof nutrients by zooplankton reduced both N and P limitationThese results support the hypothesis that zooplankton have potentiallyimportant indirect effects on phytoplankton communities throughrecycling of nutrients     

Temporal organization of phytoplankton communities linked to physical forcing

The performance of individual phytoplankton species is strongly governed by the thermal stratification’s impact on vertical mixing within the water column, which alters the position of phytoplankton relative to nutrients and light. The present study documents shifts in phytoplankton structure and vertical positioning that have accompanied intensified long-term stratification in a natural ecosystem. Ordination analysis is used to extract gradients in phytoplankton composition in Lake Tahoe, an extremely nutrient-poor lake, over a 23-year period of records. Community structure in the 1980s was associated most strongly with resource availability (low nitrogen to phosphorus ratios, deeper euphotic zone depth), while intensified stratification dominated the phytoplankton structure since the late 1990s. Within diatoms, small-sized cells increased with reduced mixing, suggesting that suppressed turbulence provides them with a competitive advantage over large-sized cells. Among the morphologically diverse chlorophytes, filamentous and coenobial forms were favored under intensified stratification. The selection for small-sized diatoms is accompanied by a shoaling trend in their vertical position in the water column. In contrast, the motile flagellates displayed a deeper vertical positioning in recent years, indicating that optimal growth conditions shifted likely due to reduced upwelling of nutrients. As the thermal stratification of lakes and oceans is strongly linked to climate variables, the present study confirms that climate warming will alter phytoplankton structure and dynamics largely through effects on nutrient availability and sinking velocities. Intensified stratification should favor the expansion of small-sized species and species with the capability of buoyancy regulation, which may alter primary productivity, nutrient recycling, and higher trophic productivity. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

台湾海峡上升流区浮游植物对营养盐添加的响应

2006年6月在台湾海峡近岸上升流区通过表层水体营养盐添加的现场培养实验,研究该海区营养盐限制情况及其浮游植物水华产生的主要影响因素.对营养盐,叶绿素a浓度和浮游植物细胞丰度进行了测定,结果表明,实验中不存在明显的硅限制;氮磷营养盐均存在明显的限制,且氮限制情况更为严重.营养盐添加后,冰河拟星杆藻(Asterionellopsis glacialis)等硅藻迅速生长成为优势藻种,其对氮磷的利用机制有所不同.对氮营养盐采取吸收后迅速同化利用,相较于硝酸盐的补充,氨氮补充条件下优势硅藻更易迅速生长并迅速死亡;对磷营养盐的利用则由于体内磷库的存在,采用迅速吸收后贮存在体内慢慢消耗的利用机制.氮营养盐的补充是上升流期间浮游植物水华产生的主要因素.     

珠江口及毗邻海域营养盐对浮游植物生长的影响

基于2006年7月(夏季),10月(秋季)和2007年3月(春季)的现场调查数据,对珠江口及毗邻海域中的营养盐和叶绿素a等环境生态因子的时空分布特性进行了对比分析,研究了氮磷比与叶绿素a含量和种群多样性之间的联系,探讨了该海域营养盐对于浮游植物生长的影响。结果表明:(1)研究海域营养盐表现出较强的季节和空间差异性,总氮(TN)和总磷(TP)浓度均值春季(1.545 mg/L、0.056 mg/L)和夏季(1.570 mg/L、0.058 mg/L)均大于秋季(1.442 mg/L、0.034 mg/L),且春夏季浓度空间差异更明显。(2)调查期间海域营养盐含量超标现象突出,夏季尤为明显。无机氮(DIN)总体均值0.99 mg/L,超四类海水标准限值1倍,活性磷酸盐(PO4-P)总体均值0.021 mg/L,DIN∶PO4-P平均值为130;叶绿素a浓度与营养盐、p H、温度有较显著的相关性。(3)叶绿素a浓度较高的站位,具有较高的DIN∶PO4-P值,但浮游植物多样性指数偏低,优势种明显,主要为中肋骨条藻。氮磷比的改变会影响不同生长特性的浮游植物间的竞争和种群结构的改变;今后海洋污染治理中,在控制氮、磷污染时要注意氮磷比的改变可能造成的浮游生态影响。     

Temperature modulated effects of nutrients on phytoplankton changes in a mountain lake

Piburger See, a dimictic mountain lake in Austria, experienced moderate cultural eutrophication in the 1950s. Lake restoration led to a re-oligotrophication in the 1990s with a decrease in seasonal phytoplankton biovolume until the late 1990s, but a reversed trend from the early 2000s onwards. We hypothesize that recent changes in phytoplankton biomass and functional structure are triggered by changes in lake nitrogen and silica concentrations, and we expect climate-related factors to modulate the trophic status of Piburger See. Phytoplankton data were analyzed by non-metric multidimensional scaling (NMDS) applied on biovolume of morpho-functional groups, combined with correlation analyses of environmental variables. Since the 2000s, short-term changes in phytoplankton of Piburger See were explained by varying concentrations and ratios of nitrogen and silica, while the inter-annual variability in phytoplankton species composition was rather attributed to superimposed rising water temperature and lake thermal stability. Our results underline the co-dominant role of phosphorus and nitrogen as phytoplankton drivers in lakes that experience periods of nitrogen limitation. The combined impact of nutrients and climate on phytoplankton development can thus mimic short-term increases in the trophic level of less productive lakes.     

沿岸海域富营养化与赤潮发生的关系

综述了赤潮的发生与沿岸海域富营养化的关系。近几十年来,人类活动使得天然水体的富营养化进程大大加速。营养负荷的增加与高生物量水华的增多相联系。控制营养输入后,浮游植物生物量或有害藻类水华事件也相应减少。营养的组成与浮游植物的种类组成及水华的形成有密切联系。有机营养对有害藻类水华的促进作用受到关注。营养输入时机影响浮游植物种间竞争的结果,因而对浮游植物的群落演替具有深远影响。由于浮游植物存在生理差异,因而对营养加富的反应因种而异。营养在调控某些有毒藻类的毒素产量方面也发挥着重要作用。此外,营养输入与藻类水华之间存在复杂的间接联系。当然,营养状况并非浮游植物群落演替的唯一决定因素。研究结果提示,控制营养输入、减缓水域富营养化是减少有害藻类水华发生的有效途径,而深入研究典型有害藻类的营养生理对策则为防治并最终消除有害藻类水华提供了理论基础。     

Effects of nutrient recycling by zooplankton and fish on phytoplankton communities

In laboratory experiments we tested the hypothesis that nutrients supplied by fish and zooplankton affect the structure and dynamics of phytoplankton communities. As expected from their body size differences, fish released nutrients at lower mass-specific rates than Daphnia. On average, these consumers released nutrients at similar N:P ratios, although the ratios released by Daphnia were more variable than those released by fish. Nutrient supply by both fish and Daphnia reduced species richness and diversity of phytoplankton communities and increased algal biomass and dominance. However, nutrient recycling by fish supported a more diverse phytoplankton community than nutrient recycling by Daphnia. We conclude that nutrient recycling by zooplankton and fish have different effects on phytoplankton community structure due to differences in the quality of nutrients released. Received: 21 December 1998 / Accepted: 31 May 1999     

The influence of mesozooplankton on phytoplankton nutrient limitation: a mesocosm study with northeast Atlantic plankton

We used marine phytoplankton from mesocosms seeded with different zooplankton densities to study the impact of mesozooplankton on phytoplankton nutrient limitation. After 7 d of grazing (copepod mesocosms) or 9 d (appendicularian mesocosms) phytoplankton nutrient limitation was studied by enrichment bioassays. After removal of mesozooplankton, bioassay bottles received either no nutrients, phosphorus or nitrogen alone, or a combination of nitrogen and phosphorus and were incubated for 2 d. Phytoplankton reproductive rates in the bottles without nutrient addition were calculated after correction for grazing by ciliates and indicated increasing nitrogen limitation with increasing copepod abundance. No nutrient limitation was found in the appendicularian mesocosms. The increase of nutrient limitation with increasing copepod density seems to be mainly the result of a trophic cascade effect: Copepods released nanoplankton from ciliate grazing pressure, and thereby enhanced nitrogen exhaustion by nanophytoplankton and reduced nitrogen excretion by ciliates. Nitrogen sequestration in copepod biomass, the mechanism predicted by the ecological stoichiometry theory, seems to have been a weaker effect because there was only little copepod growth during the experiment.     

Contrasting responses of phytoplankton and benthic algae to recent nutrient enrichment in Arctic tundra ponds

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Variability of nutrient limitation in the Archipelago Sea,SW Finland

Over a two year study period, zooplankton was sampledin Gazi Bay, Kenya, using a 335 μm mesh size Bongonet. Two Way Indicator Species Analysis (TWINSPAN)classification technique demonstrated that rainfalland tidal regime had substantial influence on thezooplankton community structure. Samples collectedduring the rainy season months clustered together whentreated with TWINSPAN. Furthermore, theclustering was more pronounced for neap tidesamples than for spring tide ones. Samples obtainedduring spring tide did not give a clear cut pattern. Canonical Correspondence Analysis (C.C.A.) confirmedthese findings, a clustering together of rainy/neaptide samples; and little separation (based onenvironmental variables) between samplingstations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Patterns of seasonal phytoplankton distribution in prairie saline lakes of the northern Great Plains (U.S.A.)

Seasonal changes in freshwater phytoplankton communities have been extensively studied, but key drivers of phytoplankton in saline lakes are currently not well understood. Comparative lake studies of 19 prairie saline lakes in the northern Great Plains (USA) were conducted in spring and summer of 2004, with data gathered for a suite of limnological parameters. Nutrient enrichment assays for natural phytoplankton assemblages were also performed in spring and summer of 2006. Canonical correspondence analysis of 2004 data showed salinity (logCl), nitrogen, and phosphorus (N:P ratios) to be the main drivers of phytoplankton distribution in the spring, and phosphorus (C:P ratios), iron (logTFe), and nitrogen (logTN) as important factors in the summer. Despite major differences in nutrient limitation patterns (P-limitation in freshwater systems, N-limitation in saline systems), seasonal patterns of phytoplankton phyla changes in these saline lakes were similar to those of freshwater systems. Dominance shifted from diatoms in the spring to cyanobacteria in the summer. Nutrient enrichment assays (control, +Fe, +N, +P, +N+P) in 2006 indicated that nutrient limitation is generally more consistent within lakes than for individual taxa across systems, with widespread nitrogen and secondary phosphorus limitation. Understanding phytoplankton community structure provides insight into the overall ecology of saline lakes, and will assist in the future conservation and management of these valuable and climatically-sensitive systems.     

Nutrient limitation of phytoplankton in a naturally acidic lake (Lake Caviahue, Argentina)

As a result of a low pH, the inorganic carbon of acidic lakes is present as CO₂ at air-equilibrium concentration and is substantially lower than the inorganic carbon concentration in higher-pH waters with bicarbonate. This situation is quite common in artificially acidified lakes and where inorganic carbon is considered the limiting factor in phytoplankton growth. Apart from low inorganic carbon content, Lake Caviahue in Argentina has low nitrogen and high phosphorus content. The aim of this work was to assess the importance of inorganic carbon, phosphorus, and nitrogen, relating data on lake nutrients to phytoplankton species requirements. Lake samples taken in the 2004–2006 period did not show any particular trend in the vertical distribution of the water column of ammonium, inorganic carbon, and phosphorus with reference to either seasonality or depth. A decrease of some 15% in the lake’s phosphorus concentration was observed over the same period. Although the total phytoplankton biomass in Lake Caviahue was similar throughout the period, a seasonal variation was observed. Lab bioassays were carried out with solutions of bicarbonates, ammonium, nitrates, and phosphate. We worked with three species separately, namely, two chlorophytes, Keratococcus rhaphidioides and Watanabea sp.; and one euglenophyte, Euglena mutabilis. Answers to specific nutrient requirements differed for each algal species: both chlorophytes prefer ammonium or nitrates added on their own, whereas the euglenophyte registered a higher growth rate with the joint addition of ammonium and phosphorus. Even when the limiting nutrient(s) for phytoplankton yield and rate varied between species, we observed a tendency for nitrogen limitation in Lake Caviahue.     

The influence of a dissolved inorganic nitrogen gradient on phytoplankton community dynamics in a chain of lakes

In a chain of lakes along which nutrient availability varies in a gradient, we performed factorial nutrient enrichment experiments to determine if nitrogen limitation was the principal factor controlling the differences in phytoplankton biomass, photosynthetic productivity, diversity, and species composition among two of the lakes in the chain. In the least productive lake, East Graham Lake, P and C enrichments (in the absence of N enrichment) had no effect on biomass and diversity, whereas within two weeks the N enrichments (alone or in any combination with P and/or C) increased the biomass and decreased the diversity of East Graham Lake phytoplankton to levels similar or identical to those in more productive Shoe Lake. Short-term ¹⁴C photosynthetic rates in East Graham Lake water also responded only to N in the third week. However, photosynthesis was stimulated by P in the first week, and a few species did increase in numbers with P enrichment, suggesting that some degree of P limitation remains in addition to the strong N limitation in East Graham Lake. A number of species responded individually to the enrichments in a manner similar to that of the overall community, and a strong overlapping of discriminant analysis scores for N-enriched East Graham Lake with those of Shoe Lake was consistent with our prediction that the community structure of N-enriched East Graham Lake water would shift toward that of Shoe Lake. However, many species did not respond consistently with these results, and the nutrients tested were clearly not a major factor in the differences in abundance of those species among the two lakes. The results support the argument that overall biomass production and diversity of the phytoplankton community in a lake can be a relatively simple function of a single most-limiting nutrient. However, many of the species responses also confirm that, while nutrient availability is an important factor in the control of the species composition of the community, other factors are likely to prevent reliable predictions of all species effects on the basis of nutrient availability alone.     

Transition from P‐ to N‐limited phytoplankton growth in an artificial lake on flooded cutaway peatland in Ireland

Question: Which nutrient limits primary production in a lake created by flooding industrial cutaway peatland? Location: Clongawny Lake (53°10’N, 07°53’W), County Offaly, Ireland Methods: Nutrient concentrations in lake water and the dynamics of phytoplankton populations were monitored over a 38‐month period. The ratio of dissolved inorganic nitrogen to total phosphorus (DIN:TP) and nutrient enrichment bio‐assays were used to investigate temporal changes in nutrient limitation. Results: Primary production in the new lake was phytoplankton‐driven due to the scarcity of recolonizing macrophytes. Phytoplankton growth was initially phosphorus‐limited. The runoff of phosphate fertilizer from an adjacent coniferous forestry plantation raised the TP concentration of lake water 5.5‐fold. Consequently, the biovolume of phytoplankton increased 30‐fold, and chlorophyll‐a concentrations increased eightfold, reaching hyper‐eutrophic levels. A concurrent depletion of nitrogen in lake water reduced the DIN:TP ratio from 17.8 to 0.6, and phytoplankton growth rapidly became nitrogen‐limited. Phytoplankton composition shifted from dinoflagellates to minute, unicellular chlorophytes, with a coincident decline in species diversity. Cyanobacteria did not proliferate, most likely due to the acidic nature of the lake. Conclusions: Results illustrated the vulnerability of newly created cutaway peatland lakes to developing severe phytoplankton blooms and coincident secondary nitrogen limitation in the presence of moderate external phosphorus inputs.     

Long term study on the influence of eutrophication, restoration and biomanipulation on the structure and development of phytoplankton communities in Feldberger Haussee (Baltic Lake District, Germany)

Feldberger Haussee provides a classic example of eutrophication history of hardwater lakes in the Baltic Lake District (Germany) and of changes in their algal flora during the 20th century. The lake originally was regarded as slightly eutrophic. A process of drastic eutrophication from the 1950s until the end of the 1970s caused mass developments of blue-green and green algae. A restoration program was started in the 1980s to improve the water quality of the lake using both diversion of sewage outside the catchment area, and biomanipulation by altering the fish community. This restoration program led to positive changes in the lake ecosystem. Direct effects of biomanipulation resulted in an increase of herbivorous zooplankton, a decrease of phytoplankton biomass, and an increase of water transparency. The recovery of Feldberger Haussee also may have been indirectly enhanced by an increase in nutrient sedimentation as a consequence of intensified calcite precipitation, decrease in phosphorus remobilization due to a pH-decrease, increased NIP-ratio, and recolonization of the littoral zone by macrophytes. This paper concentrates on the long term development of the phytoplankton community as a response to changes in the food web structure as well as to alterations in the chemical environment of the algae. Both are reflected in four major stages passed by the algal assemblage between 1980 and 1994: (1) From 1980-summer 1985 dense green algal populations were found indicating similar conditions as in the 1970s during the period of maximum eutrophication. (2) A diverse phytoplankton community during summer 1985–1989 showed the first effects of a recovery. (3) From 1990–1992 the phytoplankton was characterized by ungrazeable filamentous blue-green algae first of all as a response to increased herbivory of zooplankton on edible species and to increasing N/P-ratios. (4) Finally, the algal species diversity increased in 1993 and 1994 whereas the phytoplankton biomass decreased showing the success of the combined restoration measures.