Sea Drainage Area Research Articles

Productive and Environmental Consequences of Sixteen Years of Unbalanced Fertilization with Nitrogen and Phosphorus—Trials in Poland with Oilseed Rape, Wheat, Maize and Barley

Two factorial field experiments were carried out between 2003 and 2018 in the Experimental Stations in Eastern and Western Poland using four crop rotations with winter oilseed rape, winter wheat, maize and spring barley. The initial value of phosphorus (P) in Grabów soil was 69.8 mg P·kg−1 soil and in Baborówko soil it was 111.3 mg P·kg−1 soil (Egner-Riehm Double-Lactate DL). P fertilizer was added annually at 39 kg P·ha−1 under winter oilseed rape, 35 kg P·ha−1 under maize and 31 kg P·ha−1 under wheat and barley using superphosphate and nitrogen (N), which was added at five levels (30–250 kg N·ha−1) per year as ammonium nitrate in addition to controls with no added fertilizer. Through the several years of the experiment, P fertilizer had no effect on crop N use efficiency (NUE) nor crop productivity. There was significant soil P mining particularly in the high-N fertilizer trials causing a reduction in the content of available soil P by up to 35%. This work recommends that, based on soil P analysis, P fertilizer should not be added to high-P soils. This practice may continue uninterrupted for several years (16 in this case) until the excess soil P has been reduced. This mechanism of removal of “legacy” P from soil has major implications in reducing runoff P into the Baltic Sea drainage area and other water bodies.

Cryptic diversity and mtDNA phylogeography of the invasive demon shrimp, Dikerogammarus haemobaphes (Eichwald, 1841), in Europe

The regions of the Black, Caspian, and Azov seas are known for being both (i) the place of extensive crustacean radiation dated to the times of Paratethys and Sarmatian basins, and (ii) present donors of alien and invasive taxa to many areas worldwide. One amphipod morphospecies,Dikerogammarus haemobaphes, is known both as native to rivers draining to the Black and Caspian seas as well as a successful invader (nicknamed demon shrimp) in Central and Western European rivers. Based on mitochondrial (COI and 16S) and nuclear (28S) datasets and 41 sampling sites, representing both the native (19) and the invaded (22) range, we assessed cryptic diversity, phylogeography and population genetics of this taxon. First, we revealed the presence of two divergent lineages supported by all markers and all species delimitation methods. The divergence between the lineages was high (18.3% Kimura 2-parameter distance for COI) and old (ca. 5.1 Ma), suggesting the presence of two cryptic species withinD. haemobaphes. Lineage A was found only in a few localities in the native range, while lineage B was widespread both in the native and in the invaded range. Although genetic divergence within lineage B was shallow, geographic distribution of 16S and COI haplotypes was highly heterogeneous, leading us to the definition of four Geo-Demographic Units (GDUs). Two GDUs were restricted to the native range: GDU-B1 was endemic for the Durugöl (aka Duruşu) Liman in Turkey, whereas GDU-B2 occurred only in the Dniester River. GDU-B3 was both present in several localities in the native range in the Black Sea drainage area and widespread in Central and Western Europe. The GDU-B4 was found exclusively in the Moskva River in Russia. Extended Bayesian Skyline Plot indicated steady growth of GDU-B3 population size since 30 ka, pointing to the rather old history of its expansion, first in the late Pleistocene in the native range and nowadays in Central and Western Europe. The analysis of haplotype distribution across the present distribution range clearly showed two invasion routes to Central and Western Europe. The first one, originating from the lower Dnieper, allowed the demon shrimp to colonize Polish rivers and the Mittellandkanal in Germany. The second one, originating from the Danube delta, allowed to colonize the water bodies in the upper Danube basin. The UK population has originated from the Central Corridor, as only a haplotype found exclusively along this route was recorded in the UK. Population genetics analysis showed that the invasion of the demon shrimp along the Central Corridor was not associated with the loss of genetic diversity, which might contribute to the success of this invader in the newly colonized areas.

The current threat level of fish in river network of individual sea-drainage areas in the Czech Republic

Abstract The assessment of changes in the population spread of individual ichthyofauna species (lampreys and fishes) as well as the identification of unfavourable impacts is the necessary prerequisite for the correct selection of corrective measures. The river network in the Czech Republic belongs to the three sea-drainage areas (North Sea, Baltic Sea, and Black Sea). The species composition of the original ichthyofauna and the extent of the threat to some species differs in the individual sea-drainage areas. The original ichthyofauna in the Czech Republic consists of 4 lamprey species and 55 fish species. Out of this, only one lamprey species and 31 fish species originate in all three sea-drainage areas. There are 37 fish species considered as the original ones in the North Sea drainage area, there of 4 species are EX, 1 species EW, and 11 species (29.7%) are threatened. In the Baltic Sea drainage area, there are 4 species EX, 1 species EW, and 8 species (22.8%) threatened out of the total 35 assessed species. Out of 49 species in the Black Sea drainage area, there are 4 species EX and 23 species (46.9 %) threatened. The most important reasons considered as the causes of the disappearance or reduction in the presence of some fishes are the water pollution, adjustments to water flow beds, the limitation of floods in alluvial areas, the permanent river basin fragmentation, and the spread of invasive species. Out of these factors, the only positive change has been noticed in the pronounced decrease in water flow pollution after 1990. Angling is also considered as the set of targeted bio manipulation which purposefully and often one-sidedly influences fish populations for the benefit of species being interesting for the angling sport.

Historical occurrence and extinction of Atlantic salmon in the River Elbe from the fourteenth to the twentieth centuries

Abstract Data on the occurrence, biology, and historical background of the Atlantic salmon, Salmo salar L., (Pisces, Salmoniformes) in the Elbe river basin (Europe, North Sea drainage area) with a focus on Bohemian territory (Central Europe) from the fourteenth to twentieth centuries are summarized in this paper. Historical methods of salmon fishing in Central Europe and historical legal protection of salmon in Bohemia are presented. The salmon is a model example of species which was extirpated as a result of anthropogenic changes in the landscape and rivers in some water systems. The human activities, such as stream bed regulation, dam system construction, other migration barriers, water pollution, fisheries exploitation, that led to the extirpation of Atlantic salmon in the Elbe river basin (are discussed. The last sporadic migrating native salmon were registered in the Bohemian section of the Elbe river basin in the mid twentieth century.

Cryptic invasion of Baltic lowlands by freshwater amphipod of Pontic origin

Gammarus varsoviensis is morphologically close to G. lacustris, with which it is often misidentified. Geographic range of G. varsoviensis includes Germany, Poland, Lithuania, Latvia, Belarus and Ukraine. Such a distribution pattern led us to the assumption that the species might have originated in the Black Sea drainage area. From there, as early as the nineteenth century, it could possibly have migrated to the Baltic basin through the Pripyat-Bug canal. Thus, the goals of this study are: (1) to indicate the level of genetic divergence of G. varsoviensis from the morphologically closest species – G. lacustris and (2) to investigate the possibility of the Pontic origin of G. varsoviensis and its range expansion across the Black Sea/Baltic Sea watershed to Central Europe through the artificial canal network. Altogether 128 partial 16S rDNA sequences of Gammarus varsoviensis from 19 localities were gained. They were analysed in conjunction with a sequence of G. lacustris obtained in this study from the Dnieper system and sequences of G. lacustris, G. pulex and G. fossarum available in GenBank in order to estimate the relationships among the species. GenBank accession numbers for all the haplotypes defined within this study are: G. varsoviensis – from JN641868 to JN641875; G. lacustris – JN641876. The genetic distance within and between the species was calculated, as well as phylogenetic relationships among haplotypes, which were inferred with Neighbor-Joining method. The haplotype relationships were analysed with the Minimum Spanning Network. Also mismatch distribution of the haplotypes were tested under sudden expansion model and sequence deviations from selective neutrality. Neighbor-Joining analysis revealed that G. varsoviensis and G. lacustris haplotypes formed separate well defined clades. Mean genetic diversity between the two species was ca. 15× higher than the intraspecific distance and similar to the value obtained for G. fossarum/G. pulex species pair. Therefore, G. varsoviensis can be definitely considered as a distinct species from G. lacustris. Among 128 sequences obtained from G. varsoviensis, 8 haplotypes were identified and grouped into two clades: one found only in the lower Dnieper (two haplotypes) and the second one encompassing the rest of haplotypes observed in the upper Dnieper and Baltic Sea basin. Only one haplotype was found in the Baltic Sea drainage area. A mismatch distribution curve as well as selective neutrality tests demonstrated sudden expansion model. Our findings suggest that G. varsoviensis is an alien gammarid that originated in the Pontic area. Its expansion in Central Europe apparently started soon after the opening of the artificial waterways joining the Black and the Baltic Sea drainage basins.

Import–export balance of nitrogen and phosphorus in food, fodder and fertilizers in the Baltic Sea drainage area

Nitrogen (N) and phosphorus (P) are essential elements for life, but in excess they contribute to aquatic eutrophication. The Baltic Sea is a brackish semi-enclosed sea that is heavily influenced by anthropogenic loading of nutrients, resulting in a major environmental problem, eutrophication. In this study, the nutrient balance of the food production and consumption system in seven countries in the Baltic Sea drainage area was quantified for the period 2002–2005. The food production and consumption system accumulates nutrients in the Baltic Sea drainage area, due to extensive imports to the system. The average annual net surplus of nutrients was 1 800 000 tons N and 320 000 tons P in 2002–2005, or annually 28 kg N and 5 kg P per capita. The average total annual import was 2 100 000 tons N and 340 000 tons P during 2002–2005. The largest imports to the system were fertilizers, totaling 1 700 000 tons N and 290 000 tons P. Traded nutrients in food and fodder amounted to a net annual surplus of 180 000 tons N and 25 000 tons P. The nutrient load to the Baltic Sea due to the food consumption and production system was 21% N and 6% P of the respective annual net inputs to the region. This study shows that large amounts of nutrients to Baltic Sea drainage area are inputs from outside the region, eventually contributing to eutrophication. To reduce the nutrient imports, fertilizers should be used more efficiently, nutrients should be recycled more efficiently inside the region, and food system should be guided toward low-nutrient intensive diets.

Sustainable governance of the agriculture and the Baltic Sea — Agricultural reforms, food production and curbed eutrophication

Agricultural production and nutrient loads to the Baltic Sea are likely to increase following Poland's and the Baltic States' entrance into the EU. According to HELCOM these trends will be highly dependent on the agricultural policies of the EU. The expansion of the EU can be seen as a window of opportunity where agricultural policy could improve the Baltic Sea environment. Longstanding initiatives with local organic food systems and Ecological Recycling Agriculture (ERA) in the eight EU-countries in the Baltic Sea drainage area were evaluated during 2001–2004. The empirical results were scaled up to calculate environmental impact and food production for three different scenarios. In one scenario the Baltic Countries and Poland convert their agriculture following the average Swedish production. This resulted in 58% increase of nitrogen and 18% increase in phosphorus surplus, a corresponding increase in the load to the Baltic Sea and increased food production. In two other scenarios agriculture production in the whole Baltic Sea drainage area converts to ERA. This halved the nitrogen surplus from agriculture and eliminated the surplus of phosphorus. In these scenarios food production would decrease or remain stable depending on strategy chosen.

The freshwater snails of the genus Bythinella Moquin-Tandon (Gastropoda: Rissooidea: Hydrobiidae) from Montenegro

New records of freshwater snails of the genus Bythinella Moquin-Tandon from Montenegro are presented. Bythinella dispersa, 1973 and B. luteola Radoman, 1976 are recognized and defined as separate species; B. taraensis n. sp., which lives partially sympatric with B. dispersa in the canyon of the River Tara, is described as new. All Bythinella spp. in Montengro inhabit the Dinaric part of the Black Sea drainage area, while it is practically absent from the Adriatic drainage area.

The first record of Anisus vorticulus (Troschel, 1834) (Gastropoda: Planorbidae) in Croatia?

A threatened planorbid gastropod Anisus vorticulus (Troschel, 1834), listed in the EU Habitat Directive, was found in the Krka National Park in Croatia in August 2009. This find is the first known record at least in the western part of Croatia belonging to the Adriatic Sea drainage area.

Crustacean invasions in the Estonian coastal sea

INTRODUCTION Together with habitat loss and climate change, invasions of nonindigenous species are one of the most serious threats to global biodiversity. This human-aided process has initiated significant, unpredictable, and irreversible changes to both the abiotic and the biotic environment and has caused severe economic damage in a variety of waterbodies worldwide (e.g. Canton, 1996; Vitousek et al., 1997; Sala et al., 2000). Concurrently with this global trend several new crustacean species have also been found in the Estonian coastal sea in recent years. The gammarid amphipod Gammarus tigrinus Sexton originates from the North American coast of the Atlantic Ocean. The species was introduced to Europe probably in ballast water and was first discovered in England in 1931 (Chambers, 1977). Although G. tigrinus was found in the Baltic Sea already in 1975, its significant range expansion started in the 1990s (Jazdzewski et al., 2002, 2005; Szaniawska et al., 2003). In the northern Baltic Sea G. tigrinus was first found in the northern Gulf of Riga (Herkul et al., 2006) and the northern Gulf of Finland in 2003 (Pienimaki et al., 2004). In 2005, G. tigrinus was found in the Neva Estuary, the easternmost part of the Gulf of Finland (Berezina, 2007). This species has caused a significant decrease in the diversity and density of native amphipods in the southern Baltic Sea (Grabowski et al., 2006) and Estonian coastal sea (Kotta et al., 2006; Orav-Kotta et al., 2009). The amphipod Chelicorophium curvispinum (Sars) originates from large rivers connected to the Black Sea and the Caspian Sea. It was found in the Baltic Sea already in the 1920s (Bij de Vaate et al., 2002). The species invaded to the Baltic and North seas through rivers and canals attached to the hulls of ships and in ballast water. Regardless of its long invasion history in the Baltic Sea, C. curvispinum was not found in the northern Baltic until 2005 when it was detected in the eastern part of the Estonian coast of the Gulf of Finland (Herkul & Kotta, 2007). In the next year, 2006, C. curvispinum was found in Luga Bay, Russia (Malyavin et al., 2008). Similarly to C. curvispinum, the gammarid amphipod Pontogammarus robustoides (Sars) originates from the lower reaches of Ponto-Caspian rivers and from brackish and freshwater lakes around the Black Sea (Bij de Vaate et al., 2002). In 1960-1961, the species was intentionally introduced into the Kaunas Water Reservoir on the Nemunas River, Lithuania (Bij de Vaate et al., 2002; Gumuliauskaite & Arbaciauskas, 2008). It successfully spread in the Nemunas drainage system including the Curonian Lagoon of the Baltic Sea. In 1999 P. robustoides was first found in Neva Bay, the easternmost part of the Gulf of Finland (Panov et al., 2003) and in 2006, in Lake Ladoga (Kurashov & Barbashova, 2008). In 2006 the species was recorded for the first time in the Estonian coastal sea. Similarly to G. tigrinus, P. robustoides has a potential to reduce the diversity and density of native gammarids (Panov et al., 2003; Gumuliauskaite & Arbaciauskas, 2008). The mysids Paramysis intermedia (Czerniavsky) and P. lacustris (Czerniavsky) are native to rivers connected to the Caspian Sea and Black Sea (Birshteina et al., 1968). In the 1970s P. lacustris and P. intermedia were introduced to Lake Peipsi but neither of the species has been sighted later (Timm et al., 2001). Both species were also introduced to Lake Vortsjarv, southern Estonia, in the 1970s, but only P. lacustris formed a permanent population there (Kangur et al., 2004). However, there is only a single record of P. lacustris in the Estonian coastal sea dating back to 1963 (Yarvekyulg, 1979). We are not aware of any successful introductions of P. intermedia in the Baltic Sea drainage area while P. lacustris inhabits the Curonian Lagoon, the southern Baltic Sea, already since the 1960s. In 2008 P. intermedia was found for the first time in the Baltic Sea. …

Ecological Recycling Agriculture to Reduce Nutrient Pollution to the Baltic Sea

ABSTRACT HELCOM (Helsinki Commission) has adopted a programme with a vision of a healthy Baltic Sea Environment, with diverse biological components functioning in balance, resulting in good environmental status and supporting a wide range of sustainable human economic activities. HELCOM assessments presented in the Stakeholder Conference plan of 2007 clearly show that problems with eutrophication exist in most of the sub-basins of the Baltic and that good environmental status has not been achieved. Agriculture is responsible for a large share of the leaching of nutrients to watercourses, including groundwater lakes and finally the sea. The analysis of data presented in this paper concludes that specialized agriculture with its separation of crop and animal production results in a high load of nitrogen and phosphorus to the Baltic Sea. This agricultural specialization took place throughout the Scandinavian countries after World War II and has resulted in farms with a high density of animals and great surpluses of plant nutrients concentrated to certain regions. Examples from Sweden are presented in this paper. This trend of increasing products per animal and per hectare on fewer farms and a higher surplus of nutrients on each of them is continuing in Sweden and is likely to spread to new EU member countries within the Baltic Sea drainage area with the probable consequence of increasing nutrient loads. Ecological Recycling Agriculture (ERA) is defined as an agriculture system based on local and renewable resources that integrate animal and crop production on each farm or farms in close proximity. As a result a large part of the nutrient uptake in the fodder is effectively recycled. This in effect means that each farm strives to be self-sufficient in fodder production, which in turn limits animal density and ensures a more even distribution of animals geographically. This study of 12 Swedish farms confirms earlier results that agriculture based on these principles of ecological recycling can lead to a decrease in the potential emission of reactive nitrogen by half as well as a significant reduction in the accumulation and loss of reactive phosphorus. Application of these agricultural principles throughout the Baltic region in all EU countries would result in the halving of reactive nitrogen losses and minimizing losses of reactive phosphorus. In this way the goals, set by the states of the region, could be met and the process leading to the worst-case scenario of greatly increased nutrient loads to the Baltic Sea could be stopped.

Modeling Riverine Nutrient Transport to the Baltic Sea: A Large-scale Approach

We developed for the first time a catchment model simulating simultaneously the nutrient land-sea fluxes from all 105 major watersheds within the Baltic Sea drainage area. A consistent modeling approach to all these major watersheds, i.e., a consistent handling of water fluxes (hydrological simulations) and loading functions (emission data), will facilitate a comparison of riverine nutrient transport between Baltic Sea subbasins that differ substantially. Hot spots of riverine emissions, such as from the rivers Vistula, Oder, and Daugava or from the Danish coast, can be easily demonstrated and the comparison between these hot spots, and the relatively unperturbed rivers in the northern catchments show decisionmakers where remedial actions are most effective to improve the environmental state of the Baltic Sea, and, secondly, what percentage reduction of riverine nutrient loads is possible. The relative difference between measured and simulated fluxes during the validation period was generally small. The cumulative deviation (i.e., relative bias) [Sigma(Simulated - Measured)/Sigma Measured x 100 (%)] from monitored water and nutrient fluxes amounted to +8.2% for runoff, to -2.4% for dissolved inorganic nitrogen, to +5.1% for total nitrogen, to +13% for dissolved inorganic phosphorus and to +19% for total phosphorus. Moreover, the model suggests that point sources for total phosphorus compiled by existing pollution load compilations are underestimated because of inconsistencies in calculating effluent loads from municipalities.

Holocene climate variability and cultural evolution in the Near East from the Dead Sea sedimentary record

A comprehensive record of lake level changes in the Dead Sea has been reconstructed using multiple, well dated sediment cores recovered from the Dead Sea shore. Interpreting the lake level changes as monitors of precipitation in the Dead Sea drainage area and the regional eastern Mediterranean palaeoclimate, we document the presence of two major wet phases (∼ 10–8.6 and ∼ 5.6–3.5 cal kyr BP) and multiple abrupt arid events during the Holocene. The arid events in the Holocene Dead Sea appear to coincide with major breaks in the Near East cultural evolution (at ∼ 8.6, 8.2, 4.2, 3.5 cal kyr BP). Wetter periods are marked by the enlargement of smaller settlements and growth of farming communities in desert regions, suggesting a parallelism between climate and Near East cultural development.

SUMMER INPUTS OF RIVERINE NUTRIENTS TO THE BALTIC SEA: BIOAVAILABILITY AND EUTROPHICATION RELEVANCE

Most nitrogen and phosphorus transported by world rivers to the oceans is associated with dissolved organic matter. However, organic matter as a potential source of N and P has hitherto been largely neglected in studies of coastal microbial food webs. We examined 50 rivers, draining a major part of the Baltic Sea watershed, with respect to summer concentrations, chemical composition, and biological availability of N and P. The broad spectrum of rivers studied enabled us to assess whether the input of terrigenous organic matter can be an important nutrient source, at various levels of anthropogenic loading of inorganic N and P. Concentrations of total N and P ranged from 9 to 220 μmol/L and from 0.14 to 5.56 μmol/L, respectively, with the highest concentrations in the southern part of the Baltic Sea drainage area and in several rivers on the Finnish western coast. Urea and dissolved combined amino acids (DCAA) each constituted 4–20% of dissolved organic nitrogen (DON), while dissolved free amino acids (DFAA) made up <3% of DON. The contribution of urea and amino acids to the DON pool was inversely correlated with DON concentration. Bacterial regrowth bioassays in selected rivers demonstrated that ∼30% of DON and ∼75% of dissolved organic phosphorus (DOP) was potentially available to the indigenous bacterial assemblage of the Baltic Sea, and hence susceptible to mineralization within the pelagic food web. Our study is among the first to demonstrate that bacterioplankton are able to utilize a major part of DON and DOP from a broad spectrum of natural waters. The C:N ratio, absorbance spectra, and fluorescence properties of the organic matter suggest that the observed high bioavailability of DON and DOP was due to a large contribution of organic matter from riverine primary production compared to the humic matter derived from terrestrial vascular plants. In addition, algal and bacterial cells dominated the transport of particulate organic material, further enhancing productivity of coastal waters. No correlations were found between DON bioavailability and the fraction of DON bound in urea and amino acids, indicating a utilization of other N compounds (e.g., amides) by the bacteria. We estimate that the input of summer riverine N to the Baltic Sea consists of 48% dissolved inorganic N, 41% DON, and 11% particulate N. Corresponding values for phosphorus are 46%, 18%, and 36% of dissolved inorganic P, DOP, and particulate P, respectively. During the thermal summer stratification, when freshwater inputs are trapped in the surface layer, rivers contribute ∼30% of N and ∼5% of P needed to support the export production (plankton sedimenting out of the photic layer) in the Baltic Sea. The high availability to bacteria suggests that DOP is a major stimulator of pelagic productivity in the P-limited northern part of the Baltic Sea. Based on reported concentrations in other areas, we suggest that the global contribution of riverine organic N and P to the primary production of coastal waters is comparable to the contribution of inorganic nutrients.

The Baltic Basin Case Study—towards a sustainable Baltic Europe

Four watersheds, each characterized by a major resource use were selected for the study: The Vistula River in Poland—agriculture; the Dalälven River in Sweden—forestry; the Archipelago Sea in Sweden, Finland, Estonia—tourism; and the Lake Peipsi in Estonia/Russia—fisheries/agriculture. The main objective was to examine the reactions of particular ecosystems within the Baltic Sea drainage area, and to assess sustainability conditions on the regional level. The degree of sustainability and impact on the Baltic Sea were investigated through workshops and seminars in the areas. Overviews of environmental and socio-economic conditions were succinctly summarized in commissioned papers. Interventions by and discussions with scholars, sector experts, administrators and stakeholders of the various sites laid the foundation for conceptualizing the interaction of natural and human forces for each case. The project was able to draw quite a number of conclusions, summarized as the following lessons learnt. In the Vistula Region, nutrient emissions have levelled off but shortage of freshwater is critical. Forestry in the Dalälven watershed is largely environmental-friendly, except for fragmentation of the landscape and its negative impact on biodiversity. In the Archipelago area a former low-energy community has been replaced by a leisure time society. Different types of tourism is developing, but despite this variety, an improved integration of ecological properties with socio-economic patterns is required in order to build a sustainable, living Archipelago. The lake Peipsi basin and the surrounding area suffer both from problems of resource management and economic backwardness. Parts of the local economy has lost access to the one time large Soviet market, although the Estonian side has apparently benefited from present economic growth. To cope with the division of the lake, a regime for trans-national management is unfolding. It is based on both informal and, to an increasing extent, agreed professional contacts. Networks of engaged people were in all sites a resource for and promoter of the sustainability path. In order to succeed and to maintain the zeal, they need strong institutional support and common goals. Public programmes in the Baltic, ie. the work of the Helsinki Commission and Baltic Agenda 21, have developed instruments to enhance sustainability beneficial for the management of these watersheds. But critical tasks remain to be done in developing a shared understanding of ways to improve management of ecosystems with social factors.

ESTIMATION OF RIVERINE LOADS OF NITROGEN AND PHOSPHORUS TO THE BALTIC SEA, 1970-1993

This article presents the results of the first critical examination of time series of riverine nutrient-load data for the entire Baltic Sea drainage area. Water quality data collected by or for the different national environmental agencies were compiled and analysed statistically to identify and remove inconsistent or obviously incorrect observations. Moreover, sampling tours were undertaken to acquire additional information about the present nutrient concentrations in the largest rivers in the study area. Gaps in the time series of approved data were then filled in by employing statistical interpolation and extrapolation methods. Thereafter, the concentration and runoff data were combined to obtain estimates of monthly nutrient loads for the time period 1970–93. The results of the calculations showed that although there had been substantial changes in land use, atmospheric deposition and wastewater treatment in many parts of the study area, the total riverine loads of nitrogen (N) and phosphorus (P) to the Baltic Sea have been fairly constant since 1980, and most likely also since 1970. Moreover, the interannual variation was clearly correlated to the runoff. The mean annual loads for the time period 1980–93 were found to be about 825 000 tonnes N and 41 000 tonnes P, respectively. This implies that (i) several other investigators have strongly underestimated the riverine loads of nutrients, especially the nitrogen, and that (ii) the riverine loads by far exceed the input to the Baltic Sea from other sources, {i.e.} atmospheric deposition, direct emissions from cities and industries along the Baltic Sea coast and nitrogen fixation by marine algae.

Rules of protection of Gulf Sea waters in Poland in the light of international co-operation within Helcom

In Helsinki, on 22 March 1974, the governments of the countries in the Baltic region signed an agreement on cooperation in the protection of the marine environment — “Convention on the Protection of the Marine Environment of the Baltic Sea Area”, the so-called Helsinki Convention. This gives rise to international cooperation comprising scientific research, changes in national legal and organizational structures, and implementing detailed commitments. In Poland, inhabited by almost half of the population in the Baltic Sea drainage area and which uses almost 40% of the arable land of the region, the effects of the activities undertaken are of considerable importance for the ecological situation of that sea. The paper presents, on the example of one of coastal provinces — the Gdańsk province and the Gulf of Gdańsk — the problems of the land — sea interaction, the activities undertaken in monitoring the coastal marine waters, the pollution loads discharged from land sources, implementation of international commitments as well as the results of these activities in the form of changes in the environment.