Late Holocene water-level changes in Lake Iso Lehmälampi, Southern Finland, reflected in subfossil Cladocerans and Chironomids

Anal y ses of subfossil cladocerans (Crustacea: Cladocera) and chi rono mids (Diptera: Chironomidae) were ap plied to ex am ine wa ter-level changes in a small and oligotrophic lake in south ern Fin land over the past 2000 years. Ma jor changes in the in ver te brate com mu ni ties oc curred ca. 400 AD on wards when the lit to ral cladoceran Alonella nana started to re place the plank tonic Eubosmina as the dom i nant spe cies and chi rono mids Psectrocladius sordidellus group and Zalutschia zalutschicola in creased. These changes were most likely due to a de creas ing wa ter level and an en larg ing pro por tion of the lit to ral area, pro vid ing suit able veg e ta tive hab i tats, e.g. aquatic bryophytes (mosses), for these taxa. The low er ing wa ter level reached its min i mum just be fore the Me di eval Warm Pe riod, ca. 800–1000 AD, af ter which the lake level rose again and re mained high un til mod ern times. A prom i nent change in the chi rono mid as - sem blages oc curred dur ing the 20th cen tury when Ablabesmyia monilis and Chironomus anthracinus type in creased, pre sum ably due to changes in wa ter chem is try, caused by anthropogenic load of pol lut ants.