Nutrient limitation in Crater Lake,Oregon

Experiments were carried out to determine what nutrient (or nutrients) was primarily responsible for limiting phytoplankton productivity in ultraoligotrophic Crater Lake. The experiments included in situ and laboratory nutrient addition bioassays utilizing the natural phytoplankton community, Selenastrum capricornutum bottle assays, photosynthetic responses, photosynthetic carbon metabolism, and response of dark uptake of ¹⁴CO₂ with the addition of NH ₄ ⁺ . The results suggested that a trace metal(s) or its availability was the primary factor limiting the epilimnetic phytoplankton productivity. Nitrogen was extremely low, and quickly became limiting with the addition of trace metals and a chelator. Iron is the most likely candidate as the limiting nutrient. Trace metals and nitrogen are also both important in limiting phytoplankton at 100 m, a depth where biologically mediated turnover of nutrients seems to be more important.     

Nutrient limitation and algal blooms in urbanizing tidal creeks

Tidal creeks are commonly found in low energy systems on the East and Gulf Coasts of the United States, and are often subject to intense watershed human development. Many of these creeks are receiving urban and suburban runoff containing nutrients, among other pollutants. During the period 1993-2001, we studied three tidal creeks located in southeastern North Carolina, a rapidly urbanizing area. All three creeks received anthropogenic nutrient loading. Oligohaline to mesohaline stations in upper tidal creek regions had much higher nutrient (especially nitrate-N) concentrations than lower creek areas, and hosted spring and summer phytoplankton blooms that at times exceeded 200 μg chlorophyll a l⁻¹. Phytoplankton biomass during winter was low at all stations in all three creeks. Spring and summer nutrient addition bioassay experiments were conducted to characterize the nutrients limiting phytoplankton growth. Water from high salinity stations in all three creeks always showed significant positive responses to nitrate-N inputs, even at concentrations as low as 50 μg N l⁻¹. Low salinity stations in upper creek areas often showed significant responses to nitrate-N inputs, but on occasion showed sensitivity to phosphorus inputs as well, indicating the influence of anthropogenic nitrate loading. During several experiments, one of the upper stations showed no positive response to nutrient inputs, indicating that these stretches were nutrient replete, and further phytoplankton growth appeared to be light-limited either by phytoplankton self-shading or turbidity. Water from upper creek areas yielded much higher chlorophyll a concentrations in bioassay experiments than did lower creek water. In general, these urbanizing tidal creeks were shown to be very sensitive to nitrogen loading, and provide a physical environment conducive to phytoplankton bloom formation in nutrient-enriched areas. Tidal creeks are important ecological resources in that they are considered to be nursery areas for many species of fish and shellfish. To protect the ecological function of these small, but very abundant estuarine systems, management efforts should recognize their susceptibility to algal blooms and focus on control of nonpoint source nutrient inputs, especially nitrogen.     

Nutrient pulsing as a regulator of phytoplankton abundance and community composition in Galveston Bay, Texas

Galveston Bay, Texas, is a large shallow estuary with a watershed that includes 60% of the major industrial facilities of Texas. However, the system exhibits low to moderate (2-20 μg l⁻¹) microalgal biomass with sporadic phytoplankton blooms. Both nitrogen (N) and phosphate (P) limitation of phytoplankton growth have been proposed for the estuary. However, shifts between N and P limitation of algae growth may occur due to annual fluctuations in nutrient concentrations. The primary goal of this work was to determine the primary limiting nutrient for phytoplankton in Galveston Bay. Nutrient addition bioassays were used to assess short-term (1-2 days) phytoplankton responses (both biomass and community composition) to potentially limiting nutrients. The experimental bioassays were conducted over an annual cycle using natural water collected from the center to lower part of the estuary. Total phytoplankton biomass increased in the nitrate (10 μM) additions in 11 of the 13 bioassays, but no significant increases were detected in the phosphate (3 μM)-only additions. Bioassay results suggest that the phytoplankton community was usually not phosphate limited. All major groups increased in biomass following nitrate additions but diatoms increased in biomass at a faster rate than other groups, shifting the community composition toward higher relative abundance of diatoms. The results of this study suggest that pulsed N input events preferentially favor increases in diatom biomass in this estuary. The broader implications of this study are that N pulsing events, primarily due to river discharge, play an important role in structuring the phytoplankton community in the Galveston Bay estuary.     

Nutrient limitation of phytoplankton in a central Arizona reservoir

The influence of added nutrients nitrogen, phosphorus and carbon on the phytoplankton of a small recreational reservoir in central Arizona was investigated during the summer, 1974. Polyethylene bags were used to isolate lake water and the natural populations for the addition of nitrogen, phosphorus and carbon individually and in combination. A large increase in phytoplankton numbers, extractable chlorophyll, pH and dissolved oxygen occurred only in bags to which both nitrogen and phosphorus were added, suggesting that both nitrogen and phosphorus levels were limiting to the primary producers. Little alteration in species composition resulted from the addition of the above nutrients.     

Nutrient limitation of phytoplankton production in Alaskan Arctic foothill lakes

We used 54 enrichment bioassays to assess nutrient limitation (N, P) of ¹⁴C uptake by natural phytoplankton assemblages in 39 lakes and ponds in the Arctic Foothills region of Alaska. Our purpose was to categorize phytoplankton nutrient status in this under-represented region of North America and to improve our ability to predict the response of primary production to anticipated anthropogenically mediated increases in nutrient loading. Experiments were performed across several watersheds and included assays on terminal lakes and lakes occupying various positions in chains (lakes in series within a watershed and connected by streams). In total, 89% (48 of 54) of the bioassays showed significant stimulation of ¹⁴C primary production by some form of nutrient addition relative to unamended controls. A significant response was observed following enrichment with N and P, N alone and P alone in 83, 35 and 22% of the bioassays, respectively. In experiments where N and P proved stimulatory, the influence of N alone was significantly greater than the influence of P alone. Overall, the data point to a greater importance for N than P in regulating phytoplankton production in this region. The degree of response to N and P enrichment declined as the summer progressed and showed no relationship to irradiance or water temperature, suggesting secondary limitation by some micronutrient such as iron as the summer advanced. Phytoplankton nutrient status was often consistent across lakes within a watershed, suggesting that watershed characteristics influence nutrient availability. Lakes in this region will clearly show increased phytoplankton production in response to anthropogenic activities and anticipated changes in climate that will increase nutrient loading.     

Nutrient limitation and plant species composition in temperate salt marshes

Addition of inorganic nitrogen, phosphorus and potassium in a factorial design in two ungrazed Wadden-Sea salt marshes at low and high elevations showed that nitrogen was the limiting nutrient. No effects of nutrient addition were detected in the 1st year, probably due to a considerable rainfall deficit during the growing season. In the 2nd year, which was more humid, only nitrogen addition caused significant effects in both the low salt marsh dominated by Puccinellia maritima and the high marsh dominated by Festuca rubra. No two-way or three-way interactions with phosphorus or potassium were found. In the low marsh, nitrogen addition had a negative effect on the biomass of Puccinellia, but a positive effect on the biomass of Suaeda maritima and on the total above-ground biomass. Puccinellia was replaced by Suaeda after nitrogen addition, due to shading. In the high salt marsh, no significant effects of fertilizer application on total above-ground biomass were found, due to the weak response of the dominant species Festuca rubra, which accounted for 95% of total biomass. The biomass of Spergularia maritima increased, however, as a response to nitrogen addition.The shoot length of Festuca was positively affected by nitrogen fertilization. It is suggested that stands of Festuca reached maximal biomass at the study site without fertilization and that its growth was probably limited by self-shading. Received: 22 September 1996 / Accepted: 5 April 1997     

Nutrient limitation of phytoplankton and periphyton growth in upland lakes

SUMMARY 1. Thirty small upland lakes in Cumbria, Wales, Scotland and Northern Ireland were visited three times between April and August 2000. On each occasion water chemistry was measured and phytoplankton bioassays were performed in the laboratory to assess growth‐rate and yield limitation by phosphorus and nitrogen. In addition, yield limitation of periphyton growth was investigated twice, in situ, using nutrient‐diffusing substrata. 2. Over the whole season the percentage frequency of P, N and co‐limitation was 24, 13 and 63%, respectively, for phytoplankton rate limitation and 20, 22 and 58%, respectively, for phytoplankton yield limitation. 3. A clear response of periphyton yield to nutrient additions was found in 75% of all cases and of these, co‐limitation was most common (54%). Average percentage frequency for P and N limitation was 26 and 20%, respectively. 4. Phytoplankton and periphyton showed seasonal changes in nutrient limitation within sites. In particular, co‐limitation became progressively more common as the season progressed. 5. The response of phytoplankton growth rate to ammonium and nitrate addition was identical, but ammonium was a slightly better source of nitrogen than nitrate for phytoplankton yield on 7% and for periphyton yield on 10% of the occasions. However, the magnitude of the effect was small. 6. The concentration of dissolved inorganic nitrogen (DIN) and the molar ratio of DIN to total dissolved phosphorus (TDP), appeared to be the main environmental factors controlling the extent of nitrogen or phosphorus limitation at a given site. Nitrogen limitation was more likely than phosphorus limitation where the DIN was <6.5 mmol m^?3 and the ratio of DIN : TDP was <53. Co‐limitation was the most likely outcome at a DIN concentration <13 mmol m^?3 and at a DIN : TDP molar ratio <250. Above these values phosphorus limitation was most likely. 7. The relatively high frequency of nitrogen limitation and co‐limitation at higher N : P ratios than previously reported, may result from the inability of nitrogen‐fixing cyanobacteria to thrive in these upland lakes where pH and the concentration of phosphorus tended to be low and where flushing rates tended to be high.     

Nutrient limitation of phytoplankton growth in Waquoit Bay, Massachusetts, USA: a nutrient enrichment study

We conducted nutrient enrichment experiments and field sampling to address three questions: (1) is there nutrient limitation of phytoplankton accumulation within an estuary whose waters are exposed to relatively high nitrogen loading rates, (2) where in the salinity gradient from fresh to seawater (0 to 32‰) is there a shift from phosphorus to nitrogen limitation of phytoplankton accumulation, and (3) is there a seasonal shift in limiting function of phosphorus and nitrogen anywhere in the estuarine gradient. Nitrogen and phosphorus enrichment experiments in the Childs River, an estuary of Waquoit Bay, Massachusetts, USA, showed that the accumulation of phytoplankton biomass in brackish and saline water was limited by supply of nitrate during warm months. The effects of enrichment were less evident in fresh water, with short-lived responses to phosphate enrichment. There was no specific point along the salinity gradient where there was a shift from phosphorus- to nitrogen-limited phytoplankton accumulation; rather, the relative importance of nitrogen and phosphorus changed along the salinity gradient in the estuary and with season of the year. There was no response to nutrient additions during the colder months, suggesting that some seasonally-varying factor, such as light, temperature or a physiological mechanism, restricted phytoplankton accumulation during months other than May-Aug. There was only slight evidence of a seasonal shift between nitrogen- and phosphorus-limitation of chlorophyll accumulation. Phytoplankton populations in nutrient-rich estuaries with short flushing times grow fast, but at the same time the cells may be advected out of the estuaries while still rapidly dividing, thereby providing an important subsidy to production in nearby deeper waters. This revised version was published online in August 2006 with corrections to the Cover Date.     

黄海和东海营养盐分布及其对浮游植物的限制

根据1997～1999年黄海和东海4个季节的现场调查资料,分析探讨了黄海、东海的营养盐分布特征及其对浮游植物生长的限制状况．结果表明,在长江口以东及其东北部海域终年存在一个范围很大的营养盐高值区．分析表明,这些营养盐主要来自长江冲淡水的扩展及苏北沿岸流的输送．此外,还获得了1998年长江流域特大洪水期间,迄今被观测到的长江冲淡水中营养盐的最大扩展范围,计算并研究了黄海、东海上层水中Si／N／P比值,结果表明,黄东海上层水中Si／N比值较高,Si不会成为黄东海浮游植物生长的限制因子;但在南黄海南部尤其是西南部、东海近岸及长江口以东海域,N／P比值很高(>30),说明与一般海洋环境的情况不同,黄海、东海有很大一部分海域浮游植物的生长受磷限制,而不是受氮限制．     

Nutrient limitation of two saccharolytic clostridia; secretion, sporulation, and solventogenesis

Abstract Growth of the cellulolytic acidogen Clostridium strain C7 undergoing progressive nutrient limitation has been compared with that of the solventogen Clostridium beijerinckii . On the basis of cellulase secretion, differentiation of dissimilatory metabolism, and sporulation, different survival strategies by the two clostridia in progressive nutrient limitation can be discerned. In addition, the metabolic differentiation to butanol production in Clostridium beijerinckii can be specifically associated with the sporulation stage in which the forespore is enclosed by double membranes but not by a spore coat.     

Nutrient limitation of bacterioplankton and phytoplankton in humic lakes in northern Sweden

1. Two small humic lakes in northern Sweden with concentrations of dissolved organic carbon (DOC) between 15 and 20 mg L^–1 were fertilized with inorganic phosphorus (P) and inorganic nitrogen (N), respectively. A third lake was unfertilized and served as a control. In addition to this lake fertilization experiment, data from different regional surveys were used to assess the role of different limiting factors.
2. The P fertilization had no effects on bacterioplankton or phytoplankton, while phytoplankton were significantly stimulated by N fertilization. Inorganic nutrient limitation of bacterioplankton was a function of DOC concentration in water of the investigated region and nutrient-limited bacteria were found only in lakes with DOC concentrations less than around 15 mg L^–1
3. The fertilization experiments demonstrated that the DOC-rich experimental lakes contained a bioavailable pool of P that was not utilized to its full potential under natural conditions. The overall mobilization of energy (bacterioplankton plus phytoplankton) in the experimental lakes was restricted by lack of inorganic N.     

Organic-rich bimineralic ooids record biological processes in Shark Bay,Western Australia

Marine ooids have formed in microbially colonized environments for billions of years, but the microbial contributions to mineral formation in ooids continue to be debated. Here we provide evidence of these contributions in ooids from Carbla Beach, Shark Bay, Western Australia. Dark 100–240 μm diameter ooids from Carbla Beach contain two different carbonate minerals. These ooids have 50–100 μm-diameter dark nuclei that contain aragonite, amorphous iron sulfide, detrital aluminosilicate grains and organic matter, and 10–20 μm-thick layers of high-Mg calcite that separate nuclei from aragonitic outer cortices. Raman spectroscopy indicates organic enrichments in the nuclei and high-Mg calcite layers. Synchrotron-based microfocused X-ray fluorescence mapping reveals high-Mg calcite layers and the presence of iron sulfides and detrital grains in the peloidal nuclei. Iron sulfide grains within the nuclei indicate past sulfate reduction in the presence of iron. The preservation of organic signals in and around high-Mg calcite layers and the absence of iron sulfide suggest that organics stabilized high-Mg calcite under less sulfidic conditions. Aragonitic cortices that surround the nuclei and Mg-calcite layers do not preserve microporosity, iron sulfide minerals nor organic enrichments, indicating growth under more oxidizing conditions. These morphological, compositional, and mineralogical signals of microbial processes in dark ooids from Shark Bay, Western Australia, record the formation of ooid nuclei and the accretion of magnesium-rich cortical layers in benthic, reducing, microbially colonized areas.     

Nutrient limitation of phytoplankton communities in Subarctic lakes and ponds in Wapusk National Park, Canada

We determined the limiting nutrient of phytoplankton in 21 lakes and ponds in Wapusk National Park, Canada, using nutrient enrichment bioassays to assess the response of natural phytoplankton communities to nitrogen and phosphorus additions. The goal was to determine whether these Subarctic lakes and ponds were nutrient (N or P) limited, and to improve the ability to predict future impacts of increased nutrient loading associated with climate change. We found that 38% of lakes were not limited by nitrogen or phosphorus, 26% were co-limited by N and P, 26% were P-limited and 13% were N-limited. TN/TP, DIN/TP and NO₃ ⁻/TP ratios from each lake were compared to the Redfield ratio to predict the limiting nutrient; however, these predictors only agreed with 29% of the bioassay results, suggesting that nutrient ratios do not provide a true measure of nutrient limitation within this region. The N-limited lakes had significantly different phytoplankton community composition with more chrysophytes and Anabaena sp. compared to all other lakes. N and P limitation of phytoplankton communities within Wapusk National Park lakes and ponds suggests that increased phytoplankton biomass may result in response to increased nutrient loading associated with environmental change.     

Differences in nutrient limitation and grazer suppression of phytoplankton in seepage and drainage lakes of the Adirondack region,NY, U.S.A

1. For seepage and drainage lakes of the Adirondack mountain region (NY, U.S.A) hydrologic regime is correlated with physical and chemical differences that can affect phytoplankton and planktonic food webs (e.g. presence and influence of wetlands, dissolved organic carbon concentration, anoxia, nutrient cycling). We conducted short‐term (48 h), in situ enclosure experiments to evaluate the relative importance of macrozooplankton grazing and nutrient limitation of phytoplankton biomass in small Adirondack seepage and drainage lakes (N = 18, 1–137 ha). Epilimnetic dissolved organic carbon (DOC) concentrations and pH values represented the diversity of the region. We measured chlorophyll a changes in response to grazer removal (> 120 μm) and nutrient addition (～ 10× ambient N, P, or N + P), and evaluated changes with respect to in situ light, temperature, NO₃, NH₄, SRP, and crustacean assemblage characters. 2. Nutrient addition stimulated significant increase in chlorophyll a concentration at 11 of 18 sites (GLM, Tukey–Kramer). Phytoplankton of clearwater drainage lakes were P‐limited, whereas clearwater and brownwater seepage lakes responded to additions of N and/or N + P. Relative light availability explained half the variance in response to nutrient addition in drainage (r2 = 0.48), but not seepage lake experiments (P > 0.05). 3. We observed responses to grazer removal at eight of 18 sites, usually clearwater drainage lakes. Crustacean grazing may be as significant as nutrient limitation of [chl a] for many drainage lake phytoplankton assemblages. Responses were related to in situ density of zooplankton only in drainage lakes. Light explained some variability in response to grazer removal for drainage (r2 = 0.35) and seepage lake experiments (r2 = 0.35). 4. These experiments provide evidence that hydrology may ultimately play an important role in determining nutrient and grazer regulation of phytoplankton. Proximate mechanisms affecting our results may be associated with differences in wetland vegetation, [DOC], and nutrient cycling.     

太平洋中西部海域浮游植物营养盐的潜在限制

2009年8月至9月期间在太平洋西部N1站和中部N2站进行现场营养盐加富培养实验。结果显示:N1站,浮游植物生物量对N或者P添加都有较强的响应,其中N+P+Si组和N+P组浮游植物长势迅速,叶绿素a从初始的0.03μg/L分别达到2.12μg/L和1.83μg/L,同时P先于N和Si之前被耗尽;说明N1站为N、P共同限制,P是首要限制因子。而N2站,浮游植物生物量仅对N、P共同添加有明显响应,N先于P和Si被浮游植物消耗殆尽。利用培养过程中营养盐比值变化推断,N1站浮游植物以低于Redfield ratio(16N∶1P)吸收N和P;而N2站浮游植物以高于Redfield ratio(16N∶1P)吸收N和P。这可能解释了太平洋西部的寡营养盐海域为潜在P限制,而在太平洋中部海域则为潜在N限制。     

Diurnal variation of phytoplankton in Loch Lomond

A study of diurnal variation over a 48 hour period was undertaken in July 1973 to ascertain the extent and timing of some major chemical, physical and biological variables in Loch Lomond. The phytoplankton population was dominated by the diatom Tabellaria fenestrata, with a maximum abundance between 04.00 and 06.00 h in surface waters on both days. A distinct diurnal variation in cell numbers was also recorded. Chlorophyll a values also showed a regular pattern of variation with a single peak between 10.00 and 14.00 h each day. Some chemical changes appeared to be a direct consequence of phytoplankton multiplication. Nitrate-nitrogen showed a decrease in concentration coinciding with the period of cell multiplication, whereas dissolved silica concentrations only fell on the completion of this process. Other common diatoms displayed less distinct patterns of variation although Fragilaria crotonensis attained its maximum abundance in surface waters. Considerable variation was recorded in the number of organisms and chlorophyll a levels at 25 cm intervals in the upper metre of the water column, with large variations in standing-crop and chemical parameters in the space of one hour. Diurnal oscillations in the position of the thermocline were recorded, with the thermal discontinuity being at its greatest depth in the early hours of the morning. The hypolimnion and thermocline regions clearly acted as a source of nutrient supply to the epilimnion. From this investigation it is apparent that for the proper understanding of diurnal variation a 24 hour study alone is insufficient and may give rise to misleading results.Department of Botany, University of GlasgowDepartment of Botany, University of Glasgow     

Effects of low nitrogen-phosphorus ratios in the phytoplankton community in Laguna de Bay, a shallow eutrophic lake in the Philippines

The effects of low nitrogen-phosphorus ratios on microalgae from a large eutrophic freshwater lake in the Philippines were investigated. Natural microalgal populations from Laguna de Bay, the largest lake in the Philippines, were cultured using three different nitrogen-phosphorus weight ratios (2N:1P; 6N:1P and 12N:1P) at two phosphorus concentrations (0.25 and 0.5 mg l^–1) in each case. The growth and genera composition of the cultures under the different treatments were followed for a 12-week period. Community level responses were assessed based on species richness (s), Shannon-Wiener Index (H), Simpson Index () and Evenness (J). Among the different microalgal groups, only the chlorophytes showed a significantly higher density in response to the 12N:1P treatment at the higher P concentration, indicating that the nutrient ratio had a significant interaction with the nutrient levels used in the experiments. The genera found in the different treatments were generally similar; however, the degree of dominance of some varied with treatment during the experiment. The succession of dominant genera also differed among the N:P treatments. The diatoms like Fragilaria, Aulacoseira (= Melosira) and Nitzschia dominated the lowest N:P. On the other hand, chlorophytes (Kirchneriella and Scenedesmus) dominated the highest N:P treatment, particularly from the second to the seventh week of the experiments with the diatoms becoming co-dominant only towards the eighth week until the end of the experimental. The 6N:1P treatment showed a mixed dominance between the diatoms and the chlorophyte genera. The various indices of diversity indicate significantly lower diversity only in the 12N:1P at 0.5 mg l^–1 P and not in 12N:1P at 0.25 mg l^–1 P.     

Nutrient limitation along a productivity gradient in wet meadows

Conservation management in meadows often focuses on reducing soil fertility and consequently community productivity as to promote and sustain species-rich vegetations. The productivity level to which nutrients are limiting growth is, however, unclear, as well as the relationship between productivity and the type of nutrient limitation. We carried out a fertilization experiment with N, P and K in six annually mown meadows along an aerial phytomass gradient (200–650 g m^–2). All meadows were found to be growth-limited by nutrients. Low-productive meadows were N-limited, or N+P co-limited, whereas our higher productive meadows were co-limited by a combination of N, P and/or K. The results from our experiments were compared with the results from 45 other fertilization experiments with N, P and K in grasslands and wetlands (aerial phytomass range 50–1500 g m^–2). Our results were consistent in nitrogen being the most frequent (co)-limiting nutrient, and regarding the equal frequence of occurrence of P (co)-limitation and K (co)-limitation (both in ca. 25–30% of all sites). Co-limitation occurred more often in our sites than in the other experiments. There was no clear relationship between aerial phytomass and type of nutrient limitation, except that K (co)-limitation only occurred at sites with phytomass above 200 g m^–2, and P (co)-limitation below 600 g m^–2. A comparison of productivity and nutrient concentrations in aerial phytomass among two years indicated that the type of nutrient limitation is not a static site characteristic but may vary with dynamic environmental conditions such as soil wetness; drought seems to enhance N-availability which may induce P- and K-limitation.     

The role of zooplankton in the ecological succession of plankton and benthic algae across a salinity gradient in the Shark Bay solar salt ponds

The relatively low biodiversity and simple hydrodynamics make solar salt ponds ideal sites for ecological studies. We have studied the ecological gradient of the primary ponds at the Shark Bay Resources solar salt ponds, Western Australia, using a coupled hydrodynamic ecological numerical model, DYRESM–CAEDYM. Seven ponds representative of the primary system were simulated with salinity ranging from 45 to 155 ppt. Five groups of organisms were simulated: three phytoplankton, one microbial mat plankton, and one zooplankton as well as dissolved inorganic and particulate organic nitrogen, phosphorus, and carbon. By extracting the various carbon fluxes from the model, we determined the role that the introduced zooplankton, Artemia sp., plays in grazing the particulate organic carbon (POC) from the water column in the high salinity ponds. We also examined the nutrient fluxes and stoichiometric ratios of the various organic components for each pond to establish the extent to which observed patterns in nutrient dynamics are mediated by the presence of Artemia sp. Model results indicated that Artemia sp. grazing was responsible for reduced water column POC in the higher salinity ponds. This resulted in an increase in photosynthetic available radiation (PAR) reaching the pond floor and consequent increase in microbial mat biomass, thus demonstrating the dual benefits of Artemia sp. to salt production in improved quality and quantity. In contrast, this study found no direct link between Artemia sp. and observed changes in planktonic algal species composition or nutrient limitation across the salinity gradient of the ponds. 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     

盐碱池塘浮游植物初级生产力日变化的研究

用黑白瓶测氧法对盐碱池塘浮游植物初级生产力的日变化进行了研究．结果表明,盐碱池塘浮游植物初级生产力存在着明显的日变化,其分布规律与光照、温度、浮游植物现存量等环境因子的变化是相关的．用黑白瓶法连续曝光24h测定初级生产力结果大大偏低于每次曝光2h的全天累积结果．对养鱼池而言,在10：00—14：00时曝光4h再推算全天的初级生产力较为适当．