Realization of the project for Acipenser oxyrhynchus oxyrhynchus restoration in the basin of the Neman River

The results of the works on the international project for the Baltic sturgeon restoration in the basin of the Neman River are considered. The mutual goal of the project is the restoration of the Baltic sturgeon population in its whole former area in the Baltic Sea. Successful works on the restoration of the Baltic sturgeon population are conducted in the Oder and the Vistula basins. The stockings of the Neman River with the sturgeon fry were started from 2012 year. It is contemplated that the sturgeon stockings of the main rivers of the Baltic Sea will enable to restore local sturgeon populations in these river basins. Till the beginning of the XXI century it was supposed that the Atlantic sturgeon Acipenser sturio had inhabited the Baltic Sea, but numerous genetic analysis of the samples of the sturgeon bones from the archeological finds in the museums showed that the Baltic Sea had been inhabited with Acipenser oxyrhynchus and its population still inhabits several rivers in Canada. This discovery permitted to start the creation of the Baltic sturgeon broodstock. Sturgeon fry from the eggs imported from Canada were used for stocking at the first stage of the project. Later it is contemplated to use the fry from the broodstocks in Germany and Poland. Sturgeon fry hatched from Canadian eggs in Poland and reared in Lithuania was used for the Neman River stocking. The fry were tagged and released in the Neris and the Sventoji Rivers in the Neman River basin. The sturgeon migrated into the Curonian lagoon where the monitoring of the catches was fulfilled. The results of sturgeon catches monitoring are discussed.     

Nitrogen budgets of the Polish agriculture 1960–2000: implications for riverine nitrogen loads to the Baltic Sea from transitional countries

The Oder and the Vistula rivers are responsible for about 25% of the total riverine nitrogen input to the Baltic Sea and of this 60% have been estimated to originate from diffuse sources. In this study we have tested the hypothesis that changes in agricultural practices in Poland have changed the riverine nitrogen export from the rivers Oder and Vistula to the Baltic Sea. We calculated agricultural long-term nitrogen budgets (1960–2000) for the catchments of the Oder and the Vistula rivers. Poland went through severe economical changes in the early 1990s, which led to a drastic decrease in fertilizer consumption. The role of the calculated nitrogen surplus as an eutrophication capacitor and the potential to reduce this important capacitor to improve the environmental state of the Baltic Sea is discussed. N surplus for the entire country showed a maximum in 1980 (58 kg ha⁻¹ sown area⁻¹) and it dropped to 39 kg ha⁻¹ sown area⁻¹ in 2000. The surplus was, however, up to two times lower than that in other transitional countries, and much lower than in Western Europe with intensive agriculture. An observed decrease in nitrogen concentrations in both Polish rivers is not ascribed to drop in fertilizer use, but it results from nutrient removal in municipal wastewater treatment plants with tertiary treatment facilities. Comparison of trends in nitrogen concentrations in different transition countries indicates that factors other than reduced fertilizer application influenced the inertia of the water quality response. Hence, the potential to reduce diffuse nitrogen emissions from agriculture by reducing fertilization is constricted in areas with low-nitrogen surplus. In transitional countries like Poland the largest potential for nutrient reductions seem to be in improving the connectivity to waste water treatment plants with tertiary treatment.     

基于“源-汇”景观的饮用水源地非点源污染风险遥感识别与评价

非点源污染因分布广泛、产生过程复杂、防治困难,近年成为影响饮用水源地水环境的重要污染源。以海南三亚赤田水库为例,开展了基于"源-汇"景观的非点源污染风险遥感识别与评价分析。首先,采用高分辨率遥感影像分类提取水源地不同类型景观分布信息;结合"源-汇"对污染的促进\\阻碍作用,在考虑影响污染物迁移的"河道距离"因子、坡度因子情况下,利用非点源污染风险指数的计算实现对区域非点源污染风险的快速识别;并基于洛伦兹曲线分析水源地景观空间分布对非点源污染的影响。结果表明:一方面,流域非点源污染风险总体较低,"汇"景观占主导作用的子流域占整个区域的76.50%;污染风险呈现东高西低的特点,极高风险区主要分布于以居住用地、建设用地等"源"景观类型为主的流域东南部区域,占整体区域面积的1.28%,而西部以林地为主污染风险小;另一方面,基于坡度因子的"源""汇"景观污染负荷之比值大于1,"源"景观在低坡度区域分布范围广,景观布局较合理;基于"河道距离"因子的"源""汇"景观污染负荷之比值为2.30,"源"景观在距河道近的区域分布范围大,对污染影响大,近河道区域需进一步调整景观格局以降低对非点源污染的影响。基...     

Hydrological problems of the vistula river valley near Płock

The Vistula river valley near the city of Plock is characterized by the presence of a cascade of terraces, determining the circulation of water and matter. The relationship between the surface water of the Vistula river and the alluvial groundwater is discussed.     

Aquatic biodiversity under anthropogenic stress: an insight from the Archipelago Sea (SW Finland)

The Archipelago Sea in the northern Baltic has been subjected to large-scale cultural, economic and ecological changes, especially during the last three decades. Environmental threats originate from both basin-wide sources, affecting the whole Baltic Sea, and from local sources, such as nutrient loading from nearby river outflows, intense agriculture, fish farming, ships' traffic, boating, and man's physical impacts on the landscape and seascape. Both the Åland archipelago and the Archipelago Sea have been listed as hot-spots by HELCOM, Baltic Marine Environment Protection Commission, eutrophication being the main threat to the aquatic environment. In this study we review how biological communities have reacted to an increase in man-induced multisource stresses. Changes in plankton, benthic animals, macroalgal assemblages and fish communities have been documented in most parts of the Baltic Sea since the 1970s. What remains to be understood is the importance of these structural changes for the functioning of the Archipelago Sea ecosystem under various levels of human impact.     

Origin and fate of dissolved organic matter in four shallow Baltic Sea estuaries

Coastal waters have strong gradients in dissolved organic matter (DOM) quantity and characteristics, originating from terrestrial inputs and autochthonous production. Enclosed seas with high freshwater input therefore experience high DOM concentrations and gradients from freshwater sources to more saline waters. The brackish Baltic Sea experiences such salinity gradients from east to west and from river mouths to the open sea. Furthermore, the catchment areas of the Baltic Sea are very diverse and vary from sparsely populated northern areas to densely populated southern zones. Coastal systems vary from enclosed or open bays, estuaries, fjords, archipelagos and lagoons where the residence time of DOM at these sites varies and may control the extent to which organic matter is biologically, chemically or physically modified or simply diluted with transport off-shore. Data of DOM with simultaneous measurements of dissolved organic (DO) nitrogen (N), carbon (C) and phosphorus (P) across a range of contrasting coastal systems are scarce. Here we present data from the Roskilde Fjord, Vistula and Öre estuaries and Curonian Lagoon; four coastal systems with large differences in salinity, nutrient concentrations, freshwater inflow and catchment characteristics. The C:N:P ratios of DOM of our data, despite high variability, show site specific significant differences resulting largely from differences residence time. Microbial processes seemed to have minor effects, and only in spring did uptake of DON in the Vistula and Öre estuaries take place and not at the other sites or seasons. Resuspension from sediments impacts bottom waters and the entire shallow water column in the Curonian Lagoon. Finally, our data combined with published data show that land use in the catchments seems to impact the DOC:DON and DOC:DOP ratios of the tributaries most.

     

Alien or endangered? Historical development of Chara connivens in the Baltic coastal waters and its implication for the species management

The occurrence of Chara connivens (Charophyta, Characeae) and its status in the Baltic Sea may raise controversies regarding its origin and historical dispersal pathways in the area. This study critically revises the protection status of C. connivens in the countries around the Baltic Sea, as well as its status on the red lists of endangered plant species (including the HELCOM Red List). The first reports on the presence of C. connivens in the Baltic Sea area were published in the aftermath of Carl Baenitz’s talks given in the early 1870s. Already then, the scientific community was well aware of the fact that C. connivens had been introduced as a ballast plant to the known Baltic areas of occurrence – the first known record of the species is from 1829. Since Poland is the only country where C. connivens is protected, the historical and contemporary distribution of this charophyte in the Polish coastal waters is presented against the background of the available historical and recent records of the species in the Baltic Sea. Recent reports from the second half of the 20th century and the beginning of the 21st century have confirmed a fairly common occurrence of C. connivens in Estonia, Sweden and Poland. This species still occurs on the German coast and has also been reported from Finland (the Åland archipelago). In recent decades, however, the species was considered rare in the Baltic Sea area. In Poland, C. connivens was even classified as extinct, despite earlier data on its occurrence in the Vistula Lagoon in the 1970s, where it was rediscovered in 2011. It was also found in the Szczecin Lagoon a year later. Both localities well suit Luther’s pattern of C. connivens occurrence in areas with intensive shipping and ballast discharge operations in historical times. Based on this in-depth revision of historical and current distribution, it is postulated that C. connivens, as non-indigenous, should not be red-listed in the Baltic Sea area, following the example of Finland. Moreover, its legal status in Poland of a strictly protected species should be reconsidered.     

Return of twaite shad <Emphasis Type="Italic">Alosa fallax</Emphasis> (Lacépède, 1803) to the Southern Baltic Sea and the transitional area between the Baltic and North Seas

The status of twaite shad was investigated within the Southern Baltic Sea (ICES subdivision 22–27) and transitional area between the Baltic and North Seas (division IIIa). The following sources of data were analysed: (i) commercial catch statistics and relevant publications, (ii) records from ichthyological museum collections, (iii) records from recent commercial and recreational fisheries, (iv) research fisheries with trawls. A total of 476 records of twaite shad including more than 16 million individuals were obtained for the time between the years 1836 and 2005. About 72.9% of all records originated from commercial catch statistics and publications, whereas 18.9% were received from ichthyological collections. Research fisheries provided 6.3%, and 1.9% of the records were obtained from recent commercial and recreational fisheries. Most records of twaite shad were estimated for subdivisions 24 (45.2%) and 26 (35.5%). From 1836 to 1959, 29.6% of the records date from the period until 1899. 70.4% of the records of twaite shad originate from the twentieth century until 1959. The mean annual catch of twaite shad between 1891 and 1959 amounted to 86,674 kg within subdivisions 24–26 of the Southern Baltic Sea. Catch data show an approximately 20-year-cyclicity of maximum yields and minimum catches, respectively. The maximum annual yield of twaite shad in subdivisions 24–26 (474,700 kg) was registered in 1940, the minimum annual yield was estimated in 1958 (10 kg). In the 1950s, the annual catches of twaite shad declined sharply. Until 1960 twaite shad catches and records originated mainly from the Pommeranian Bay/Pommeranian Coast and adjacent waters including the Szczecin Lagoon (subdivision 24), the Bay of Gdańsk, Vistula Lagoon and Vistula Spit (subdivision 26) and from the Curonian Lagoon and Curonian Spit (subdivision 26). The highest catches of twaite shad originated from the area of Curonian Lagoon/Curonian Spit from 1941 to 1960. Seasonal catches of twaite shad showed maximum values from May to July. From 1960 to 1989, only four records of A. fallax were registered in the Southern Baltic Sea which originated from German coastal waters in subdivisions 22 and 24. A total of 107 records of twaite shad was obtained in subdivisions 20–27 from 1990 to 2005. Most of these recent records originate from a twaite-shad stock in subdivisions 24, 25 and 26. There are indications which suggest a separate stock of twaite shad in subdivisions 20 and 21. Disappearance and recovery of twaite shad stocks were probably caused by the following factors: construction of barriers in rivers with spawning sites of twaite shad; habitat destruction in those rivers as consequence of gravel extraction and reengineering scheme to improve navigation and for flood defence purposes, water pollution in the lagoons of the Southern Baltic and in their tributaries, commercial fishery in the Southern Baltic and climatic variation in the Baltic Sea basin south of the latitude of 60° N. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: S. Dufour, E. Prévost, E. Rochard & P. Williot Fish and diadromy in Europe (ecology, management, conservation)     

Peculiarities of the state of phytoplankton in the Baltic Sea’s Vistula Lagoon at the turn of 21st century

In 1989–2005 the qualitative composition and seasonal and inter-annual dynamics of the total biomass of phytoplankton, chlorophyll a content, hydrological, and hydrochemical parameters were studied in the Russian zone of the Vistula Lagoon in the Baltic Sea. The results of these observations were compared to the data obtained in the 1950s and 1970s. The structural reorganization of phytoplankton was revealed, testifying to the negative changes in the ecosystem under conditions of anthropogenic pollution and eutrophication, climate warming, and increasing salinity.     

Population genetic structure after 125 years of stocking in sea trout (<Emphasis Type="Italic">Salmo trutta</Emphasis> L.)

Stocking can be an effective management and conservation tool, but it also carries the danger of eroding natural population structure, introducing non-native strains and reducing genetic diversity. Sea trout, the anadromous form of the brown trout (Salmo trutta), is a highly targeted species that is often managed by stocking. Here, we assess the present-day population genetic structure of sea trout in a backdrop of 125 years of stocking in Northern Germany. The study area is characterized by short distances between the Baltic and North Sea river watersheds, historic use of fish from both watersheds for stocking, and the creation of a potential migration corridor between the Baltic and North Sea with the opening of the Kiel Canal 120 years ago. A survey of 24 river systems with 180 SNPs indicates that moderate but highly significant population genetic structure has persisted both within and between the Baltic and North Sea. This genetic structure is characterized by (i) heterogeneous patterns of admixture between the Baltic and North Sea that do not correlate with distance from the Kiel Canal and are therefore likely due to historic stocking practises, (ii) genetic isolation by distance in the Baltic Sea at a spatial scale of <?200 km that is consistent with the homing behaviour of sea trout, and (iii) at least one genetically distinct Baltic Sea river system. In light of these results, we recommend keeping fish of North Sea and Baltic Sea origin separate for stocking, and restricting Baltic Sea translocations to neighbouring river systems.     

Rare and asymmetrical hybridization of the endemic Barbus carpathicus with its widespread congener Barbus barbus

In endemic species that co-occur with widespread congeners, hybridization can lead to an influx of novel and beneficial genetic variation, but high rates of introgression may cause genetic swamping of the endemic species and have detrimental effects on its survival potential. This study examines hybridization between sympatric populations of the Carpathian barbel Barbus carpathicus , a recently discovered cryptic species with a restricted range, and the widespread common barbel Barbus barbus . Based on six diagnostic allozyme loci, a microsatellite locus and mtDNA, hybrids were found to be present at multiple localities within the Vistula River drainage (Baltic Sea) as well as in the Tisza River system of the Danube River drainage (Black Sea). However, the numbers of hybrids were very low; four individuals of 230 fish sampled from the Vistula drainage. Bayesian assessment of their nuclear genotypes suggested that two hybrids in the Vistula drainage and nine in the Tisza system were F₁ generation, and one in the Vistula drainage and one in the Tisza system were backcrosses (BC) to B. barbus , while no F₂ or BC to B. carpathicus were detected. No hybrid carried B. carpathicus mtDNA and cytonuclear linkage disequilibria showed significant positive associations between hybrid genotypes and B. barbus mtDNA, suggesting unidirectionality in the interspecific mating with a disproportionate contribution of B. barbus mothers. Despite geographically broad occurrence of hybrids, these data provide evidence of strong constraints on hybridization in the native breeding habitats and the lack of introgression towards B. carpathicus .     

Evidence of a hybrid-zone in Atlantic cod (Gadus morhua) in the Baltic and the Danish Belt Sea revealed by individual admixture analysis

The study of hybrid zones is central to our understanding of the genetic basis of reproductive isolation and speciation, yet very little is known about the extent and significance of hybrid zones in marine fishes. We examined the population structure of cod in the transition area between the North Sea and the Baltic Sea employing nine microsatellite loci. Genetic differentiation between the North Sea sample and the rest increased along a transect to the Baltic proper, with a large increase in level of differentiation occurring in the Western Baltic area. Our objective was to determine whether this pattern was caused purely by varying degrees of mechanical mixing of North Sea and Baltic Sea cod or by interbreeding and formation of a hybrid swarm. Simulation studies revealed that traditional Hardy-Weinberg analysis did not have sufficient power for detection of a Wahlund effect. However, using a model-based clustering method for individual admixture analysis, we were able to demonstrate the existence of intermediate genotypes in all samples from the transition area. Accordingly, our data were explained best by a model of a hybrid swarm flanked by pure nonadmixed populations in the North Sea and the Baltic Sea proper. Significant correlation of gene identities across loci (gametic phase disequilibrium) was found only in a sample from the Western Baltic, suggesting this area as the centre of the apparent hybrid zone. A hybrid zone for cod in the ecotone between the high-saline North Sea and the low-saline Baltic Sea is discussed in relation to its possible origin and maintenance, and in relation to a classical study of haemoglobin variation in cod from the Baltic Sea/Danish Belt Sea, suggesting mixing of two divergent populations without interbreeding.     

The diversity and longitudinal changes of zooplankton in the lower course of a large, regulated European river (the lower Vistula River, Poland)

The diversity and longitudinal variation of zooplankton in the lower Vistula River were analyzed. Samples were taken from 40 stations located along a 272-km long section of the lower river course. During the study the unique technique of taking samples from “the same water” was used. The zooplankton community was dominated by rotifers and nauplii — larval stages of copepods. The most abundant species were: Brachionus angularis, Brachionus calyciflorus and Brachionus budapestiensis. The zooplankton species diversity in the main channel of the lower Vistula River was similar to other large European rivers; however, its abundance was lower. The diversity, abundance and biomass of potamoplankton steadily decreased downstream. This could be related both to scarcity of storage zones for potamoplankton development in the river due to the extensive regulation processes, and changes in hydrological conditions of the main channel (by the straightening of riverbed) where the samples were collected.     

Analysis of fish parasitofauna in Vistula Lagoon (the Baltic Sea)

The characteristics of parasitofauna (81 species) of 15 fish species from Vistula Lagoon (the Baltic Sea) are given. Parasites with a direct developmental cycle dominate. Parasites with a complicated developmental cycle are represented mainly by species developed through zoobenthos. Some of the parasites testify to the deterioration of the ecological state of the lagoon. A zoogeographic analysis of fish parasitofauna has shown the presence of five faunistic complexes. In Vistula Lagoon freshwater species dominate, but marine species are also recorded. Species that appeared in the lagoon as a result of human commercial activity are also registered.     

Lateral plate morph differentiation of freshwater and marine populations of the three-spined stickleback, Gasterosteus aculeatus, in Poland

The distribution of three main lateral plate morphs of the three–spined stickleback, Gasterosteus aculeatus , in the Polish zone of the Baltic Sea and inland waters is surveyed. Most sites are characterized by predominance of the completely plated morph, although it is only in the Vistula River drainage basin where monomorphic complete populations prevail. Polymorphic populations with a high proportion of the non–complete morphs are found in Puck Bay (the Baltic) and in south–west Poland, Possible causes of this pattern are discussed.     

太行山中低山区河谷内农田斑块特征及其分布格局—以河北省阜平县胭脂河主流河谷为例

以景观生态学原理为指导,调查了位于太行山中低山区的河北省阜平县胭脂河主流河谷,对河谷内农田斑块的特征及其分布格局进行了分析,结果表明,农田斑块了作河流源头外贯穿整个河谷,从上游向下游,人为活动的增加使农田的比重不断增加,导致自然景观减少,环境异质性降低,农田斑块破碎化和蔼减小,胭脂河河谷总面积为2297.09hm^2,构成河谷景观主体的农田有117个斑块,面积为1027.78hm^2,占河谷面积的44．74％,农田基本紧靠河岸分布,处在水分条件优越但易受洪水威胁的土地带上,农田在河流两侧是非对称分布,其中左岸农田面积587.58hm^2,占57．17％,斑块的宽度呈增加的态势,但变化比较大,基本上以狭长的特征出现。     

Geographic variation in fitness‐related traits of the bladderwrack Fucus vesiculosus along the Baltic Sea‐North Sea salinity gradient

In the course of the ongoing global intensification and diversification of human pressures, the study of variation patterns of biological traits along environmental gradients can provide relevant information on the performance of species under shifting conditions. The pronounced salinity gradient, co‐occurrence of multiple stressors, and accelerated rates of change make the Baltic Sea and its transition to North Sea a suitable region for this type of study. Focusing on the bladderwrack Fucus vesiculosus, one of the main foundation species on hard‐bottoms of the Baltic Sea, we analyzed the phenotypic variation among populations occurring along 2,000 km of coasts subjected to salinities from 4 to >30 and a variety of other stressors. Morphological and biochemical traits, including palatability for grazers, were recorded at 20 stations along the Baltic Sea and four stations in the North Sea. We evaluated in a common modeling framework the relative contribution of multiple environmental drivers to the observed trait patterns. Salinity was the main and, in some cases, the only environmental driver of the geographic trait variation in F. vesiculosus. The decrease in salinity from North Sea to Baltic Sea stations was accompanied by a decline in thallus size, photosynthetic pigments, and energy storage compounds, and affected the interaction of the alga with herbivores and epibiota. For some traits, drivers that vary locally such as wave exposure, light availability or nutrient enrichment were also important. The strong genetic population structure in this macroalgae might play a role in the generation and maintenance of phenotypic patterns across geographic scales. In light of our results, the desalination process projected for the Baltic Sea could have detrimental impacts on F. vesiculosus in areas close to its tolerance limit, affecting ecosystem functions such as habitat formation, primary production, and food supply.     

Comparison of biotic index used in monitoring of 2 lotic systems in north-western Argentina

Two lotic bodies located in a subtropical semi-arid region in north-western Argentina were studied: the Arias-Arenales and the Rosario rivers. Both rivers are located in Salta Province, and belong to the high basin of river Juramento, connected to the river Río de la Plata and the Atlantic Ocean. The study was conducted between March 1997 and March 1998. The region is known by its sustained economic development and one of the highest population growth rates in the country (4% per year). The objective of this work was the assessment of organic pollution spatial gradients in both rivers, as a function of the hydrological regime (a long period of drought from May to October and floodings the rest of the year). Three groups of biotic indices were applied to characterize the level of organic pollution and were based on planktonic microalgae to evaluate water quality. The relative performance of these indices was then compared for use to biomonitoring programs. The diversity indices: Shannon-Weaver and Whilm-Dorris were not highly sensible to detect moderate pollution. The saprobity indices (Pantle and Buck and Diatom Assemblage Index of Watanabe et al.), were useful to detect intermediate levels of organic load, but their sensitivity dropped at high pollution levels. The second index precisely discriminated the most deteriorated part of river Rosario, with values between 0.3-0.7 (extreme poli-saprobity). Raw sewage discharges along the most polluted sector of river Arias-Arenales were assigned a value between 10 and 11 in both periods of the hydrological regime. Both saprobity indices consider the same indicator pollution value of species. The first one is based on the relative abundance of the species while the second one is calculated with the species relative frequency. The second index is better than the first one in considering non-dominant species that were constant in each particular environmental condition. The principal component analysis allowed a representation of time and space pollution patterns and showed the specific microalgae assemblage for all the sampling stations and for both periods in the hydrological cycle. Only the latter proved to be fully useful and correct for the biological characterization of water quality system.     

Water mites (Acari,Hydrachnidia) of water bodies of the Krąpiel River valley: interactions in the spatial arrangement of a river valley

The present study is a discussion of the interactions between different types of water bodies in the spatial arrangement of a river valley, taking into account landscape data. The Hydrachnidia assemblages in particular types of valley water bodies (oxbows, riparian pools, permanent ponds, flooded alder carrs, sedge marshes, and springs) are strongly influenced by the spatial arrangement of the water bodies in the landscape. Moreover, the formation of a fauna in a particular type of valley water body is also influenced by its origin. For example, the faunas of the oxbow lakes and riparian pools would have many characteristics in common, as these two types of water body can be characterized as originating in the river. As many as 61 species common to the valley water bodies and the Kr?piel River were noted. In the interactions between the valley water bodies and the river, the direction of migration from the former to the latter was clearly predominant. Migration in the reverse direction, from the river to the valley water bodies, took place to a far lesser degree. CCA analysis of landscape variables showed the influences of certain landscape parameters on water mites. These should be regarded as indirect influences, but as a consequence of their effects, they influence the formation of specific types of Hydrachnidia assemblages.     

太行山中低山区河谷内农田斑块特征及其分布格局——以河北省阜平县胭脂河主流河谷为例

以景观生态学原理为指导,调查了位于太行山中低山区的河北省阜平县胭脂河主流河谷,对河谷内农田斑块的特征及其分布格局进行了分析.结果表明,农田斑块除河流源头外贯穿整个河谷,从上游向下游,人为活动的增加使农田的比重不断增加,导致自然景观减少,环境异质性降低,农田斑块破碎化程度减小.胭脂河河谷总面积为2297.09hm²,构成河谷景观主体的农田有117个斑块,面积为1027.78hm²,占河谷面积的44.74%.农田基本紧靠河岸分布,处在水分条件优越但易受洪水威胁的土地带上.农田在河流两侧是非对称分布,其中左岸农田面积587.58hm²,占57.17%.斑块的宽度呈增加的态势,但变化比较大,基本上以狭长的特征出现.