Vascular Hydrophytes Research Articles

Elucidating food web structure of the Poyang Lake ecosystem using amino acid nitrogen isotopes and Bayesian mixing model

AbstractCompound‐specific isotope analysis of amino acids (CSIA‐AA) is regarded as a more advanced method of unraveling food web connections than the traditional bulk isotope approach. One of the most important assumptions of the CSIA‐AA approach is that the initial offset (β) between glutamate and phenylalanine in primary producers should remain unchanged. However, the considerable difference in β values between algae (+3.4‰) and vascular plants (−8.0‰) raises concern regarding the application of the CSIA‐AA approach for complex ecosystems that depend on both resources. In the present study, a Bayesian mixing model was used to estimate the individual contribution of basal dietary resources to each consumer of Poyang Lake, and then, the β was reevaluated to adapt to the assimilation of the individual primary producer for each consumer specimen. In general, the contributions of vascular plant‐derived resources to most consumers are consistent with their feeding behaviors. The smaller contribution of vascular plants to planktivorous fish (usually less than 20%) is biologically expected because of their feeding ecology. Using this strategy, we successfully obtained realistic trophic positions (TP) of consumers in Poyang Lake, which are significantly different from traditional TPalgae or TPvascular. For instance, the TP value of grass carp (2.04) was consistent with the feeding behavior of this fish, i.e., they primarily feed on vascular hydrophytes. Therefore, the combination of the CSIA‐AA and Bayesian mixing model provides a better understanding of food web structures, even in a complex freshwater ecosystem.

Towards a rapid assessment protocol for identifying pit lakes worthy of restoration

Before the introduction of reclamation legislation in South Africa, final cut lakes in mining areas were left without any restoration while the final excavation was not back filled. Characteristics of these lacustrine water bodies vary considerably, but they are often linear in shape, large (1–30 ha), deep (2–30 m) and have poorly developed littoral zones. With water tables often near the surface; a variety of vascular hydrophytes can colonize these bodies, thus establishing emerging wetland type ecosystems. These, man-made aquatic structures that are (unintentionally) created potentially offers some realistic and inexpensive mitigation options for some of the negative impacts associated with mining, i.e. these water bodies can become useful by yielding potentially valuable services. However, no method currently exists to compare and rank these water bodies according ecological integrity and the expected monetary value to be derived from them in order to select sites for restoration. To answer this need, we applied an index to determine the ability of these water bodies to provide useful services in their current state. The index was then used to derive estimates of the monetary value of potential services in order to allow comparison with the cost of restoring the water body in question or to compare with other pit lakes. We present a South African case study to illustrate the method. As far as could be established, this is the first attempt towards creating a rapid assessment tool as standardised way of comparing pit lakes that allows for the ranking and identification of those pit lakes worthy of restoration.

Salvinia molesta D.S. Mitch.

<i>Salvinia molesta</i> D.S. Mitch.

Six decades of changes in vascular hydrophyte and fish species in three plateau lakes in Yunnan, China

Biodiversity in the plateau lakes of Yunnan, China has decreased significantly over the past decades. To better understand this degradation, we analyzed the processes and characteristics of changes in vascular hydrophytes and fish species in three of Yunnan’s largest lakes (Dianchi, Erhai, and Fuxian). We reviewed primary literature reporting the occurrence of such species between the 1950s and 2000s. During this period, 46.3 % of native hydrophytes and 84.0 % of native fish species in Dianchi Lake had gone locally extinct, compared to 21.4 and 58.8 % in Erhai, and 11.8 and 41.7 % in Fuxian, respectively. In Dianchi alien species comprised 15.4 % of total hydrophytes and 87.5 % of total fish species, compared to 5.7 and 70.8 % in Erhai, and 11.8 and 65.0 % in Fuxian, respectively. The extinction of endemic fish species was particularly serious. The proportion of endemic fish species extinct was 90.0 % in Dianchi, 75.0 % in Erhai and 63.6 % in Fuxian. Homogenization of fish assemblages (calculated Jaccard indices) across the lakes increased during the study period in parallel with the extinction of endemics and introduction of alien species. Results showed that lacustrine conditions determined the observed changes of hydrophytes and fish species, likely reflecting anthropogenic disturbances associated with rapid economic development around the lakes. In a developing region like the plateau of Yunnan, which is rich in endemic freshwater species, the challenge is how to balance economic growth with habitat protection.

Diversity of vascular hydrophytes in the Zasavica river (Serbia): Changes after thirteen years

Zasavica is a 33.1 km-long, slow-flowing river on the southern edge of the Pannonian plain. It has been a protected natural asset since 1997, and has great value as a natural aquatic habitat. In the period between 1998 and 2010, intensive studies of the aquatic vegetation were carried out. The comparisons of results gained at the beginning of that period with those from the end, show significant differences in species composition, spatial distribution, and diversity analyzed through species richness, Shannon?s diversity index, and evenness.

Vascular Hydrophytes for Bioassay of Phosphate Enrichment in Fresh Waters: A Pilot Study

Vascular hydrophytes were shown to have the potential to be useful for straightforward, low-technology, bioassay of fresh water quality, specifically in relation to phosphate enrichment by effluent from sewage treatment works. Field-collected shoots of Elodea canadensis and Callitriche sp. made greater extension growth when incubated in canal water from downstream of discharges, indicating enrichment. This was supported by phosphate analysis and by conventional Selenastrum bioassay. Growth of shoots incubated in phosphate-augmented water from upstream of discharges equalled that in downstream water, confirming that bioassay, using vascular plants, is effective in detecting enrichment by phosphate.

Changes in aquatic macrophyte flora over the last century in Catalan water bodies (NE Spain)

Landscape and aquatic environments have suffered increasing threats over the last century with major impacts on lentic waters and, presumably, on its inhabiting life. This study aims to evaluate changes in occurrence of aquatic macrophyte flora in lentic waters in Catalonia (NE Spain), emphasizing the last 20 years, with particular reference to vulnerable species. We conducted a survey (2005–2009) identifying macrophytes from 215 lentic water bodies (from eight different geomorphological typologies) and compared the data obtained with a historical compilation (1879–2006) from the Biodiversity Data Bank of Catalonia (BDBC). Vascular hydrophyte species were present in 53.5% of the sampled water bodies and only 69.7% of species cited in the BDBC were re-sampled in the recent survey. Significant changes in species occurrence were also found, particularly for those endangered macrophytes where the ratio of re-sampling was lower (52%). Hydrophyte flora of 36 water bodies has changed over the last 20 years and richness clearly tends to decrease. However, trends are different in each typology; while richness is stable in alpine lakes, it drops for coastal lagoons, ponds and karstic lakes. The threats most correlated with hydrophyte disappearance are water extraction and regulation and desiccation/drainage. To sum up, we detect a loss of hydrophyte diversity at a local and regional scale. Conservation actions are needed to preserve remaining water bodies and flora.

낙동강 하구의 수생관속식물의 분포 변화와 수금류(고니류)의 먹이식물인 세모고랭이의 성장 변화

지난 25년간 낙동강 하구의 물리적 변화에 따른 수생관속식물의 분포 변화와 수금류의 주요 먹이식물인 세모고랭이의 성장에 관하여 2002년 4월부터 2004년 8월까지 조사하였다. 낙동강 하구의 담수역인 서낙동강과 낙동강 본류 그리고 기수역에 생육하는 수생관속식물은 총 17과 32분류군으로 1985년의 소산 종 16과 33종과 비교해 큰 변화는 없었다. 하구둑 건설 후 수체가 거의 정체되고 담수화된 낙동강 본류에서는 1985년 보고되었던 5종의 수생식물이 17종으로 크게 증가하였다. 특히 본류에 위치한 대저동 둔치의 못에서 보호식물인 가시연꽃 군락이 발견되었다. 2001년 여름에 서낙동강에서 번성하였던 부레옥잠과 물상추 군락은 더이상 관찰되지 않았으며, 이미 소실된 것으로 보고되었던 어리연꽃, 이삭물수세미, 줄말이 관찰되었다. 1983년 이후 낙동강 하구의 하안과 연안의 매립으로 습지 면적이 2,893ha 감소하였으며, 고니류의 먹이식물인 세모고랭이 군락의 감소와, 특히 용원 내만에 분포하였던 1,300ha에 이르는 수금류의 먹이식물인 거머리말 군락이 소실되어 하구 전체의 먹이 식물이 크게 감소하였다. 세모고랭이의 지상부는 4월부터 9월까지 성장하였으며, 전체 7개 조사지역 중 신자도, 명지 조사지소에서 세모고랭이의 초고가 <TEX>$30\sim40cm$</TEX>로 다른 지역<TEX>$(60\sim80cm)$</TEX> 보다 성장이 불량하였다. 괴경은 9월부터 형성되었으며, 비교적 깊은 <TEX>$25\sim40cm$</TEX>에 많이 분포하였고(55%), 총 현존량의 <TEX>$44\sim57%$</TEX>를 차지하였다. 하구의 수생관속식물 분포면적은 최근 25년간 총 2,893ha에 이르는 얕은 습지의 매립으로 인해 크게 변화하고 있으며 하구를 찾는 수금류의 분포, 환경수용력 등과 크게 상관성이 있어 앞으로 심도 있는 연구가 더욱 필요하다.의 물리화학적 특성에 따라서 결정된다. 본 연구의 결과를 보면 이러한 일반적인 원칙이 각 농약의 용탈잠재성 지수에 그대로 반영되었는데, 용해도가 높고, 흡착성이 약하며 잔류성이 긴 약제일수록 대부분의 토양에서 용탈잠재성이 큰 것으로 나타났다. 토양의 특성 중에서는 특히 농약의 흡착에 직접 영향을 미치는 유기물 함량이 용탈잠재성 지수를 결정하는 중요한 요인으로 볼 수 있는데, 본 연구의 결과에서도 일반적으로 유기물 함량이 높은 화산회 토양에서는 농약의 용탈잠재성이 비화산회토양에 비교하여 낮은 것으로 나타났으며, 용해도가 높고 흡착성이 매우 낮은 약제인 metribuzin의 경우에도 투수성이 상대적으로 높은 화산회 토양에서보다 투수성이 낮은 비화산회토양에서 용탈 가능성이 높게 평가된 것으로 보아 대부분 농약의 용탈잠재성을 결정하는데 있어 토양의 투수성 보다도 유기물 함량이 더욱 중요하게 영향을 미치는 것으로 판단할 수 있다. 따라서 비화산회토를 위주로 한 유기물 함량이 낮은 토양이 분포된 지역의 지하수가 농약의 오염에 취약할 것으로 판단할 수 있으며, 이들 지역에서는 용탈잠재성이 높은 것으로 평가된 약제들의 사용을 최대한 제한함으로써 제주도 피하수의 농약 오염을 방지할 수 있을 것이다. 물론 제주도 감귤원에서는 토양의 유기물 함량과 약제의 흡착성을 우선적으로 고려하여 사용할 농약을 선택해야 할 것으로 보이나, 그 외 약제의 잔류성, 사용량, 사용시기와 함께 기후조건, 토양의 투수성, 토층이 깊이, 지하수 깊이 등의 지역적인 특성들이 농약의 용탈잠재성에 미치는 영향도 더욱 구체적으로 파악되어야 할 것이며 농약의 선택 과정에서도 이러한 특성들이 앞으로 고려되어야 할 것이다.calenol 및 citrostadienol 등이 함유(含有)되어 있었다. 6. 4-desmethylsterol fraction에 는 sitosterol (74.6%)이 주성분(主成分)을 이루고 A study on changes on the distribution of vascular hydrophytes and the growth pattern of Schenoplectus triqueter (Scirpus triqueter) was undertaken at the Nakdong River estuary from 2002 to 2004. The change was due to physical alteration of the estuary for the past 25 years. These plant species are the major food sources for winter waterfowl. A total of 32 species of vascular hydrophytes from 17 families were found in the West Nakdong River (freshwater), the main channel of Nakdong River (freshwater) and the Nakdong River Estuary (brackish water). After the construction of the barrage on the estuary in 1987, the number of hydrophytes has remarkably increased to 17 species (5 species in 1985) in the main channel of the River. In particular, a community of Eurale ferox was found at the backwater wetland of the Daejeo side of the main channel. The introduced species of Eichhornia crassipes and Pistia stratiotes that were epidemic in 2001 at West Nakdong River was not found any more. The other species such as Nymphoides indica, Myriophyllum spicatum, Ruppia spp. were rediscovered. The large area (about 1,300ha) of Zostera spp. was the main sources of food for swans, but disappeared because of direct and indirect impacts of reclamation in the River estuary. Currently, there remains a small patch of Zostera spp. and about 250ha of S. triqueter. Schenoplectus triqueter grew mostly between April-September and tuber formed, between September-October. The growth of S. triqueter up to <TEX>$60\sim80cm$</TEX> in length was observed in 5 sites out of the 7 sites in brackish area. Tubers of S. triqueter were eaten by waterfowls such as swans as winter food. In five sites, tubers took <TEX>$44\sim57%$</TEX> of total biomass in October. Tubers were found in deep layers; <TEX>$5\sim15cm$</TEX> (9%), <TEX>$15\sim25cm$</TEX> (28%), <TEX>$25\sim40cm$</TEX> (55%), below 40cm <TEX>$(6\sim7%)$</TEX>. The distribution of vascular hydrophytes has remarkably changed in the Nakdong River Estuary due to the reclamation of the area. In order to determine the extent of changes of the distribution of these plants and the carrying capacity of the area for waterfowl, an intensive research is urgently needed.

서낙동강 수질의 이화학적 특성과 수생관속식물의 분포

서낙동강의 물과 저토의 이화학적인 환경을 측정하고, 수생관속식물의 식생을 조사하였다. 수질은 수소이온농도, 용존산소, 엽록소a, 총질소 그리고 총인에 의하면 부영양화 상태이었으나 여름에는 지소에 따라 과영양 상태이었다. 수중 저토는 약산성 이었으며, 모래의 함량이 높았으나 SI는 점토, SU는 미사의 비율이 컸다. 수생식물 분포는 총 16과 26종 1변종으로 총 27분류군이었다. 지소별 우점종은 DU, GA 그리고 SU에서는 마름(Trapa japonica)이 우점하였고, DA에서는 노랑어리연꽃(Nymphoides peltata), SI는 자라풀(Hydrocharis dubia)이 우점하였다. SI와 SU에서 종다양도, 균등성이 높았으며, 우점도는 DA에서 높았다. 6월에 유입된 외래종 물상추(Pistia stratiotes)와 부레옥잠(Eichhornia crassipes)이 수역 전체에 확산되어 서낙동강 전체의 우점종이 되었다. 낙동강 하구둑 축조 당시와 비교하여 서낙동강에서 소멸된 종은 민나자스말(Najas marina), 톱니나자스말(Najas minor), 이삭물수세미(Myriophyllum spicatum), 어리연꽃(Nymphoides indica)이었다. 수생식물의 최대 현존량은 10월에 DU에서 가장 높았다(445g·Dw/㎡). 하구둑 축조당시인 1985년에 비하여 DU와 CA지소의 총현존량은 33.5%로 감소하였으며, 우점종 마름의 감소율이 56.7% 이었다. 종 수와 유사도 지수를 근거로 집괴분석한 결과에 따르면 GA-SU-DU, DA와 SI의 3집단으로 구분되어졌다. 외래종의 유입으로 인한 수생식물군락의 교란은 SI와 SU에 분포하는 가시연꽃(Euryale ferox)과 감소추세 종 자라풀을 포함하여 수역전체의 자생종들 특히 수금류의 먹이식물로 이용되는 마름, 나사말, 말즘 등의 감소를 초래하였다. The physico-chemical characteristics of water and sediment, and structures of vegetation of the vascular hydrophytes were investigated in the West Nakdong River. Water quality was eutrophic according to the mean values and the ranges of water properties such as pH, DO, BOD, chlorophyll a, total nitrogen and phosphate, and other nutrients. A few cases were hypereutrophic for chlorophyll a level in summer. Soil reaction was weak acid. Composition of sediment was mainly sand except in SI(Sinan chideung) of which was mainly clay, and SU(Suan chideung) of which was mainly silt. Flora of vascular hydrophyte had 26 species and 1 variety comprising 16 families. Trapa japonica was dominant species in the sites of DU(Dunchido), GA(Garak chideung) and SU. Nymphoides peltata and Hydrocharis dubia dominated in DA and SI, respectively. Species diversity and evenness were relatively high in SI and SU but dominance was high in DA. After June, water lettuce(Pistia stratiotes) and water hyacinth(Eichhornia crassipes) were flowed from tributary to the river. Standing crop of macrohydrophytes was high in DA from April to August, but it showed maximum standing crop (445g·dw/㎡) in DU after disturbance by explosive growth of exotic plants in October. In comparison with those in 1985, total productivities in DU and GA decreased to 33.5%, and the reduction ratio of dominant species, Trapa japonica was 56.7%. Najas marina, N. minor, Myriophyllum spicatum and Nymphoides indica have disappeared ever since the Nakdong barrage was constructed in the Nakdong river. They were divided into three groups (GA-SU-DU, DA, SI) by cluster analysis. Introduction of the exotic species in this river caused decreasing of endemic plants including endangered species Euryale ferox and rare species Hydocharis dubia, and food plants for waterfowl such as Trapa japonica, Vallisneria asiatica and Potamogeton crispus.

Makrophyten-Verbreitung und Standortqualität im eutrophen Björka-Kävlinge-Fluss (Skåne, Südschweden)

The aquatic macrophyte vegetation of the Björka-Kävlinge River (Skåne, South Sweden, Fig. 1) was investigated in 1997 and 1998. By nature, this river has a meso- to eutrophic character. Furthermore, the river has a high structural running water quality and a high species diversity over long distances. Its catchment area is dominated by agriculture and characterized by fertile calcareous soils. 219 river sections of 100–500 m length (overall length 69,950 m = 85.7% of the whole river length) between Vollsjöby and the mouth of the river into the Baltic Sea were cartographically recorded and investigated (Fig. 2). In these sections all vascular hydrophytes, amphiphytes, helophytes and some haptophytes were recorded. For the vegetation survey and evaluation of the results the methods described in Kohler & Janauer (1995) were used. The “index species” of the “limes scanicus” (H. & G. Weimarck 1985) Butomus umbellatus, Sium latifolium and others with their wide area of distribution are characteristic plants for this river type. Some plant species groups, resp. some species, show characteristic distribution patterns in the course of the river: Hildenbrandia rivularis group, Potamogeton lucens group, Zostera marina group etc. Due to the species features a classification of four floristic-ecological river zones was made (zones A to D). The distribution of the macrophyte species was also characterized by a set of quantitative parameters which are “Relative Range Length”, “Average Plant Quantity” and “Average Quantitiy Index”, respectively (Figs. 3–5). Both, the plant distribution as well as the sequences of the floristic zones are less to be seen as a consequence of a trophic gradient, but as a consequence of different river dynamics of velocity of flow, sediment quality as well as of salt water influence. The diagnostic features also served to determine the relation between plant distribution and environmental factors (shading, cattle grazing). Hildenbrandia rivularis mainly occurs in shaded areas, Elodea canadensis in unshaded ones. In sections influenced by cattle tracks there is an increased occurrence of Alopecurus geniculatus, Agrostis stolonifera and Glyceria fluitans. The reasons for the high species diversity of this eutrophic river are a relatively high water quality, a high amount of habitat structures, a variety of vegetational structures and various land use patterns in the surrounding area. Recommendations for the preservation and the improvement of the ecological conditions are made. For the conservation of the biological diversity of the river, hydraulic engineering measures should be avoided. Along considerable river sections suffering from cattle grazing, vegetation could be achieved by partial exclusion of the cattle, and in some sections buffer zones along the river should be established.

A comparitive study of the hydrophyte flora from the Alpine Rhine to the Middle Rhine. Application to the conservation of the Upper Rhine aquatic ecosystems

A typology of the main channel of the river Rhine according to its aquatic bryophyte and vascular hydrophyte assemblages is presented. The aquatic bryophytes are especially abundant in the main channel, having found stable, rocky habitats with variable water levels in the regulated river, and segregate longitudinally along a gradient of water quality. Conversely, the vascular hydrophytes are restricted to side channels with constant discharges and silt deposits, and segregate laterally along a gradient of connectivity with the main river. The hydrophytes have been affected by water eutrophication which became obvious in the 1960s–1970s. The oligotrophic groundwater-fed side-channels disconnected since the river canalization consequently include a relic reference flora. Important hydraulic works are currently in progress in order to protect the areas located downstream from the canalized Rhine from flooding by retaining the river waters in lateral systems during the discharge peaks and to recreate a functional alluvial floodplain by reconnecting the disconnected side-channels to the main river. The floodpulse caused by the suddent input of surface water in the disconnected brooks will probably wash out most of the hydrophytes and it is very likely that the rare species with their low recolonization strategies will disappear in these conditions. It is highly desirable to preserve from flooding the last oligotrophic brooks with their original hydrophyte assemblages. Those brooks which show a tendency to silt up can be re-dynamized by ecological engineering without disturbing the flowing drains of the watertable. In areas (including flowing drains of the watertable) that have already been designated for flood retention, the hydraulic works should allow, as far as possible, the preservation of the flowing oligotrophic streams by only permitting the input of surface water in the silted-up brooks. The disconnected side-channels could then continue their role as refugia from where the main channel, whose water quality has been improving for a decade, could be recolonized by its primary flora.

A taxonomic study of leaf epidermis in Korean vascular hydrophytes

A taxonomic study of leaf epidermis in Korean vascular hydrophytes

Notes on the submerged vegetation of lake Hawea

Abstract The submerged vegetation of Lake Hawea, New Zealand, was impoverished compared with that of nearby Lake Wanaka. No vascular species were found and no vegetation was present over most of the depth range normally occupied by vascular hydrophytes. The exclusion of vascular hydrophytes was apparently associated with major water level fluctuations for hydro‐electric power generation. A low diversity of charophytes and one bryophyte were recorded from Lake Hawea. Charophytes occupied a similar maximum depth, but a depressed minimum depth when compared to the equivalent community in Lake Wanaka.

Flora and Distribution of Vascular Hydrophytes from the Han River

Flora and Distribution of Vascular Hydrophytes from the Han River

Impact of encrusting carbonates on manganese, zinc and copper concentrations of two vascular hydrophytes from Texas

In alkaline calcareous waters, hydrophytes become encrusted with carbonate precipitates of a complex nature which alter bulk chemical analyses of the plants. The manganese, zinc and copper concentrations, and the ash content of two aquatic plants, Egeria densa and Potamogeton nodusus, differed considerably depending on the cleaning procedure used and, therefore, the amount of marl encrustation included in the analyses. Tapwater washed plants, retaining the marl, consistently had ash contents two to three times higher than acid-cleaned plants and exhibited higher trace metal concentrations, especially manganese.

Ultrastructural characteristics of Hydrilla leaf tissue

The general anatomy and leaf ultrastructure of Hydrilla verticillata (L.f.) Royle, a submersed vascular hydrophyte, are reported. The transversely sectioned leaf consists of only two contiguous epidermal layers, and the single midvein is composed of three to four concentric layers of cells. There are numerous intercellular spaces throughout the tissue. Electron microscopy confirmed the presence of sieve elements in the mid-vein area. P-protein, plastid inclusions and branched plasmodesmata leading into the companion cells are all considered indicative of phloem-type cells. Plastid inclusions are cuneate and lack associated starch granules, characteristics typical of monocots. The outer wall of the lower epidermis protrudes into the cell. Plant cells with wall ingrowths are termed ‘transfer cells’ and, in aquatics, function in the absorption of solutes from the external environment. In addition to the lower epidermis, spiny projections of the leaf margin could be included in this category. There is a thick fibrous layer which appears to be part of the outer wall of the upper epidermis. Secretory vesicles containing polysaccharide empty into this layer and into the wall. Cell nuclei are distinctly polymorphic. The granal arrangement, presence or absence of starch and peripheral reticulum in chloroplasts varies.

Habit, habitat, origin and geographical distribution of Chilean vascular hydrophytes

The Chilean freshwater flora consists of 54 species. A classification of its growth forms is made and the typical habitat of each of the species is analyzed. A survey is also given of their occurrence in lotic and lentic environments. The origin and geographical distribution of the different taxa are described.

Ecosystem and macrophyte primary production of the Fort River, Massachusetts

Primary production and ecosystem respiration of the Fort River ecosystem, a medium size (mean discharge 1.4 m3/sec) lowland stream in central Massachusetts, U.S.A., were measured using diurnal oxygen techniques from May 1972 to November 1973. During the summer of 1973, vascular hydrophyte production was measured with a modified cropping technique. Whole ecosystem gross primary production ranged from 0.44 g O2/m2:day in winter to 6.50 g O2/m2.day in summer, and averaged 1.78 g O2/m2.day for 12 months. Mean ecosystem respiration was 3.65 g O2/m2.day for 12 months. Mean ecosystem respiration was 3.65 g O2/m2.day. Macrophyte gross production (59.9 g O2/m2.year) constitutes 9.2% of annual ecosystem productivity and 15.2% of summer primary production. Macrophytes were little grazed and entered food webs only after death, as detritus. Decomposition occurred near the site of production at relatively rapid rates, thus transport of dead macrophyte material in stream water was low. Data from this and other stream ecosystems suggest that in general, streams are only moderately productive ecosystems which depend to varying degrees on watershed-derived organic matter inputs.

Methods for the study of the growth and production of turtle grass, Thalassia testudinum König

Research has shown that the measurement of the productivity of vascular hydrophytes by gas exchange methods is inaccurate due to the storage of gases within the leaves. Methods were developed for the study of turtle grass, Thalassia testudinum König, which allow: (a) the monitoring of the blade populations without disturbing the plant, and (b) the determination of leaf growth and net production of the blades, in addition to other biotic variables associated with the growth and development of the plant. The technique involves the marking of individual blades with a modified stapler, and the retrieval of the marked blades after a 2–3 week interval. The production measured is that which is readily available to the consumers of the Thalassia community.

Energy Flow in Bear Brook, New Hampshire: An Integrative Approach to Stream Ecosystem Metabolism

An annual energy budget is presented for Bear Brook, a small undisturbed second—order stream in northeastern United States. The ecosystem approach, in which all input and output fluxes of potential energy as organic matter are considered, is used to describe the dynamics of energy flow in a 1,700—m segment of the stream. The annual input of energy to the system is 6,039 Kcal/m2. Over 99% of this is allochthonous, from the surrounding forested watershed or from upstream areas. Autochthonous primary production by mosses accounts for less than 1% of the total energy available to the ecosystem. Algae and vascular hydrophytes are absent from the stream. Meteorologic inputs (litter and throughfall) from the adjacent forest account for 44% of annual energy input. Most of this is in particulate form. The remaining 56% of input enters by geologic vectors (inflowing surface and subsurface waters). Eighty—three per cent of the geologic input and 47% of the total input of energy occur as dissolved organic matter. Approximately 4,730 Kcal/m2 of organic detritus, nearly equally divided between leaves and branches, is stored within the system. The size of this detritus reservoir is stable from year to year. The turnover time of the branch compartment is about 4.2 years; of the leaf compartment, about 1 year. Although much of the annual input of energy is in a dissolved state, dissolved organic matter does not tend to accumulate in the system and displays a very rapid rate of turnover. Sixty—six per cent of annual energy input is exported to downstream areas in stream water. The remaining 34% is lost as heat through consumer activity. Bear Brook is a strongly heterotrophic steady—state system in which import and export of organic matter play a significant role. A conceptual scheme is presented by which import, export, photosynthesis, and respiration may be used to describe the functional dynamics and developmental processes of ecosystems.