Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Paweł Prus Inland Fisheries Institute BENTHIC MACROINVERTEBRATES IN LAKES: PROFUNDAL AND EXTRA-LITTORAL ZONE

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Ten lakes were sampled for benthic invertebrates. On these lakes 17 sites were chosen in profundal and extra-littoral zones. One site (no 1) was located in a deepest place of each lake, and on seven larger lakes the second site (no 2) was established in a second deep place. Benthic invertebrates were sampled 3 times: in February (from the ice), in April and in September. In february a pilot sampling (3 samples with Kajak’s sampler) was done on sites no 1 of 9 lakes (except the Lidzbarskie L.). In April and September 5 samples with Kajak’s sampler and 3 samples with Eckman’s sampler were taken from each site no 1 and 5 samples with Kajak’s ampler – from each site no 2. Altogether 257 samples were taken and sorted. Main taxonomic groups were identified (Chironomidae, Oligocheta and Chaoborus sp.).

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund

First benthos sampling was done in February - from ice. Photo by Sigrid Haande

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Taxonomic composition, numbers and biomass of benthic invertebrates in February In deep lakes Chaoborus larvae dominated, while in shallow ones Chironomidae usually were the most abundant taxon. Oligochaeta were found only in Lake Zarybinek.

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Benthos sampling In April and September – from a boat.

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Taxonomic composition, numbers and biomass of benthic invertebrates (data from samples taken with Kajak’s sampler). In April on sites no 1 (deepest place of each lake) only Chironomidae, Chaoborus and Oligochaeta occurred. Chironomidae dominated in shallow lakes, while Chaoborus in deeper ones.

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund In September no animals were found in 2 deepest lakes and in Lidzbarskie L. only Oligochaeta occurred. This indicates permanent oxygen depletions during summer stagnation period. Chironomidae abundance was very low in all lakes studied. Chaoborus numbers exceeded 500 individuals m -2 only in 2 lakes (Rumian and Kiełpińskie). Oligochaeta were abundant only in Lidzbarskie Lake.

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund In April on sites no 2 (less deep than no 1) Chironomidae occurred in 5 lakes, but their numbers were below 1000 individuals m -2. Chironomidae biomass was in 4 lakes grater than 10 g m -2. Chaoborus and Oligochaeta were found in 6 lakes. In Lidzbarskie lake Chaoborus was found in high numbers and Oligochaeta in very low numbers, as opposite to site no 1.

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund In September on sites no 2 Chironomidae occurred only in Kiełpińskie and Zarybinek lakes, but their numbers were very low. Chaoborus was found in all 7 lakes. In Dąbrowa Wielka and Rumian lakes its numbers were high. Oligochaeta were found in 3 lakes, in very low numbers. In Dąbrowa Wielka and Dąbrowa Mała lakes Gordiacea were noticed in very low numbers.

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund SAMPLING METHOD Kajak’s core sampler: 43 cm 2 sampling area - 5 samples/site = 215 cm 2 - Takes long samples - Quantitative method Eckman’s dredge: cm 2 sampling area - 3 samples/site = 645 cm 2 - Takes short samples - Qualitative method Standard sieve: 0.5 mm mesh size

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Chironomidae numbers were usually lower in samples taken with Eckman’s sampler, but general proportions in lakes were similar for both methods. In April only in one lake Chironomidae were found exclusively in samples taken with Eckman’s sampler, while in September in one lake they were found only in samples taken with Kajak’s sampler.

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Chaoborus numbers were slightly lower in samples taken with Eckman’s sampler, and proportions in lakes were similar for both methods. In two cases Chaoborus was found exclusively in samples taken with Eckman’s sampler, while in one case – exclusively in samples taken with Kajak’s sampler.

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Oligochaeta numbers were usually lower in samples taken with Eckman’s sampler, and proportions in lakes were similar for both methods. In April Oligochaeta presence assessed with both methods differed for some lakes. In September Oligochaeta occurred only in two lakes, and it was confirmed by both methods.

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund SUMMARY 1.Low taxonomic diversity in all lakes studied was found (up to 3 taxons). 2.Chironomidae occurred mainly on shallow sites (up to 10 m). 3.Chaoborus dominated in deep lakes, sometimes accompanied with Oligochaeta. 4.In summer in deepest lakes no benthic invertebrates were found, what indicates permanent oxygen depletions. 5.In April on shallow sites more abundant and differentiated benthic fauna than on deeper ones was found, except the Lidzbarskie Lake. 6.In September Chironomidae and Oligochaeta numbers were similar on deep and shallow sites, and Chaoborus numbers were higher on shallow sites. 7.Usually sampling with Kajak’s sampler gave higher abundance of all taxons, and only in few cases some additional taxons were found in samples taken with Eckman’s dredge. This indicates that Kajak’s sampler is sufficient for benthos assessment. 8.Uncertainty analysis can be made basing on two sampling methods used.

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund What can we learn about lake’s ecological status studying profundal or extra-littoral benthic fauna? Benthos presence / absence (except some very resistant taxa) – the indicator of strong O 2 depletions and H 2 S presence in hypolimnion – can be used for stratified lakes The Chironomidae / Oligochaeta ratio – a very rough indicator of lake’s trophic status – difficult to be used due to lack of one or both taxons in most lakes Presence of some oxygen-demanding taxa (e.g. Gammaridae) may indicate good oxygen conditions near the bottom on sites less than 10 m deep – difficult to be used due to lack of such taxons in lakes studied Benthos abundance may serve to define more precise classes (5-point scale) than obtained with presence/absence data – can be applied for stratified lakes, after some literature studies

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Benthos of the profundal zone can be used for assessment of ecological status of deep, stratified lakes. It is difficult to use the extra-littoral zone benthos for assessment of ecological status of shallow lakes.

Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Thank you for your attention