4. Chemical and Ecological Quality of Water
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4. Chemical and ecological quality of water 4.1. Rivers and lakes The assessment of the ecological status of water bodies in the category of rivers within the Venta RBD in Lithuanian part demonstrated that there are 14 water bodies (WB) at high ecological status and 27 WB - at good ecological status. The largest numbers of water bodies – 46 in the Venta RBD of Lithuanian part are at moderate ecological status as well as there is 1 water body at poor ecological status (Fig. 4.1.1). Analogous data for Latvia are showing 3 WB at high ecological status, 33 – at good ecological status, 16 – at moderate status as well as 1 at poor and 2 at bad ecological status. Rivers incompatible with at least good ecological quality status are mostly characterized by high nutrient concentrations in the water (Ntot, Ptot). For example, in Latvian part two river WB (V004 Ālande and V060 Zana) are even at bad environmental quality status due to high Ptot concentration in the first case and due to elevated Ntot concentration in the second case. Figure 4.1.1. Ecological quality status of river WB in the Venta RBD, number. Relative proportion of river WB at different quality grades in both countries is shown in the Figure 4.1.2. Lithuania has more WB at high ecological status than Latvia - 4 water bodies at high ecological status are situated in the Bartuva sub-basin, 10 – in the Venta sub-basin. Nevertheless, Lithuania has much more WB characterized as of moderate status. With respect to heavily modified water bodies (HMWB) in the category of rivers 6 Lithuanian WB meet the requirements for maximum ecological potential and the same number - for good ecological potential (Fig. 4.1.3). 5 HMWB with maximum potential are located in Venta sub-basin and 1 - in the Bartuva sub-basin. 128 As regards Latvia, there is a lower amount of HMWB in relation to rivers determined most of them reaching good ecological potential. Combining together all river WB and HMWB in both countries, Lithuania has the largest proportion of WB at highest ecological status but in the same time a very big amount of WB meeting only the moderate status (Fig. 4.1.4). In its turn, Latvian part of RBD encompasses some WB with bad quality which is not the case in Lithuania. Figure 4.1.2. Relative proportion of river WB at different ecological quality classes within the Venta RBD. Figure 4.1.3. Ecological potential of rivers concerning HMWB in the Venta RBD, number. 129 Figure 4.1.4. Relative proportion of river WB and HMWB at different ecological classes within the Venta RBD. Totally, approx. 50 % of delineated Lithuanian river WB and HMWB does not meet at least good quality criteria (Fig. 4.1.5). In Latvia such river water objects are 1/3 but it shall be mentioned that Latvia has less WB and HMWB demarcated. Figure 4.1.5. Compatibility of river WB and HMWB with at least good quality requirements within the Venta RBD, number. In order to compare the quality status of quite differing number of river water objects in both countries, the logarithmic transformation regarding numbers of various WB and HMWB is used (Fig. 4.1.6). As regards the lakes and ponds in the Lithuanian part of Venta RBD, 2 WB are at high ecological status, 4 WB are at good ecological status, 4 WB are at moderate ecological status and 1 WB - at poor ecological status. 130 Figure 4.1.6. Comparison of all quality classes in relation to river WB and HMWB within the Venta RBD in Latvia and Lithuania (logarithmic transformation of number with base „10”). With respect to Latvia, there are much more lake WB determined showing differing ecological water quality including 7 lakes even with bad quality (Fig. 4.1.7). Again, similar to rivers, incompatibility with at least good ecological quality status is mostly characterized by high nutrient concentrations in the water (Ntot, Ptot), in their turn, giving rise to high chlorophyll a concentrations and phytoplankton biomass. Especially in relatively shallow lakes, high water temperature during summer is the favourable factor as the lake rapidly heats up. In relation to Latvia very complicated situation has arisen in Valgums lake (E031), where all parameters used for assessments meet the criteria of either poor or bad quality, despite the fact that it is a lake of type 9 (relatively deep lake). Figure 4.1.7. Ecological quality status of lake and pond WB in the Venta RBD, number. 131 Relative proportion of lake WB at different quality ranks in both countries is shown in the Figure 4.1.8. Figure 4.1.8. Relative proportion of lake and pond WB at different ecological quality classes within the Venta RBD. Regarding HMWB in the category of lakes and ponds in Lithuania 1 HMWB meets the requirements for maximum ecological potential, 3 are at good ecological potential and 3 - at moderate ecological potential as well as 2 water objects – at poor ecological potential (Ubiškes pond and Lake Birţulis) (Fig. 4.1.9). In its turn, Latvia has delineated only one lake HMWB – Lake Liepāja being at poor ecological potential due to high Ntot concentration in the water. Figure 4.1.9. Ecological potential of lakes and ponds concerning HMWB in the Venta RBD, number. 132 Totally, 50 % of delineated Lithuanian lake and pond WB and HMWB does not meet at least good quality criteria (Fig. 4.1.10). In Latvia lake water objects with incompatible water quality are even more than 50 %. Figure 4.1.10. Compatibility of lake and pond WB and HMWB with at least good quality requirements within the Venta RBD, number. Comparison of all lake and pond water objects within Venta RBD in relation to their quality ranks in both countries is reflected in the Figure 4.1.11. Summary of ecological quality / ecological potential of rivers` and lakes` (ponds`) WB as well as HMWB is provided on the map in the Figure 4.1.12. In its turn, in the Figure 4.1.13 the ecological quality (potential) of cross border water bodies is reflected in a more detailed way. It must be stressed that the ecological quality assessment of WB based on Venta RBD management plans in both countries and given here shall be considered as provisional because a very limited number of biological quality elements have been implemented in the national assessment schemes and used up to now (see detailed information in the chapter 3.5). In Latvian rivers Saprobity index of zoobenthos as well as chlorophyll a concentration and phytoplankton biomass in lakes but in Lithuania – Danish Stream Fauna Index of zoobenthos and Lithuanian Fish Index in rivers as well as chlorophyll a concentration in lakes are covered. Besides, direct monitoring observations not in all WB were available. Lithuania used grouping possibility in relation to similar river WB by means of 51 monitoring stations reflecting quality status in all 104 WB. In its turn, in 27 Latvian river WB as well as in 8 lake WB the assessment was made based on expert judgment. Available anthropogenic pressure information and land use patterns have been taken into account. 133 Figure 4.1.11. Comparison of all quality classes in relation to lake and pond WB and HMWB within the Venta RBD in Latvia and Lithuania, numbers. 134 Figure 4.1.12. Summary of ecological quality and ecological potential of WB and HMWB within the Venta RBD. In addition to ecological quality of surface water the chemical status is assessed as well determining whether the average concentration of hazardous substances in aquatic environment does not exceed the ceilings set out in regulatory enactments. If the threshold is not exceeded, the chemical quality is considered as good, but if it is exceeded - as poor. First of all, monitoring should be carried out in WB where the contaminants could be discharged in significant quantities (from production of wastewater or from intensively cultivated agricultural lands). 135 Figure 4.1.13. Summary of ecological quality and ecological potential of cross border WB and HMWB within the Venta RBD. Following the provisional water quality monitoring data, concentrations of specific pollutants (hazardous substances and priority hazardous substances) exceeded the allowable norms in six places in Lithuania: in the Venta downstream of Maţeikiai, in the Varduva at Grieţa, in the Ašva at the Latvian border, in the Virvyte at Janapole, in the mouth of the Šventoji and in the Bartuva upstream of Skuodas. Later, however, no significant pollution with specific pollutants was registered in the mentioned places. Accordingly, the available monitoring data are not sufficient to prove that the rivers are currently failing good chemical status. More or less permanent monitoring of hazardous substances in Latvia was done from 2006 to 2008 in 8 Venta RBD water bodies - Bārta (V006 HM, V010), Saka (V013 HM), Venta (V027, V043, V056), Amula (V035) and Irbe (V068), where it is required by the Helsinki Convention, the ICP - Water Program1 or Decision 77/795/EEC on the water monitoring information exchange in the EU. The measurement frequency was 4-6 times per year. In its turn, none of the lake water bodies was monitored with respect to dangerous and especially dangerous substances. For assessment of chemical quality regarding dangerous and especially dangerous substances the mean annual concentrations in 2006 and 2007 as well as older data 1 The objective of ICP-Water program is to assess water acidification processes in lakes and rivers and its geographical distribution http://www.icp-waters.no/ 136 from 2003-2005 have been used2.