본 연구는 충청남도 보령시에 위치한 보령호를 대상으로 어류상 및 붕어 개체군의 특성을 파악하고자 2017년 10월부터 2018년 6월까지 조사를 실시하였다. 어류상 조사결과, 총 9과 15종 3,506개체가 출현하였으며, 한국고유종은 얼룩동사리 1종 (6.6%), 외래종 및 생태계교란종은 떡붕어, 배스 2종 (13.3%)이 조사되었다. 상대풍부도 분석결과, 빙어 1,706개체 (48.6%), 붕어 1,021개체 (29.1%)로 각각 우점, 아우점하고 있는 것으로 나타났다. 생체량 분석결과 붕어가 246,130 g으로 가장 높은 생체량을 보였으며, 동자개 50,610 g, 떡붕어 14,730 g, 메기 11,560 g, 잉어 10,930 g의 순으로 분석되었다. 군집분석 결과 우점도지수 0.87 (±0.2), 다양도 지수 0.78 (±0.5), 균등도지수 0.47 (±0.2), 풍부도지수 0.99 (±0.5)로 분석되었다. 붕어 개체군의 전장 - 체중 상관관계 분석결과 회귀계수 b값은 3.06으로 나타났으며, 비만도 지수 (K) 기울기는 양의 기울기로 분석되었다. 전장빈도분포 분석결과, 당년생은 출현하지 않았으며, 2년생으로 추정되는 170~190 mm 개체는 다수 출현하였고, 4~5년생으로 추정되는 230~280 mm 개체는 낮은 출현을 나타내었다. 보령호의 저수량 추이를 확인하기 위해 연평균저수량과 NDWI 분석을 실시한 결과, 2013년에서 2014년에 급격한 연평균 저수량 변화를 나타내었으며, 웅천천이 유입되는 St. 4에서 수위변동에 영향을 받는 것으로 추정되었다.

The objective of the study was to determine nutrition regime and limitation in the Boryeng Reservoir where there’s a water tunnel between Geum River and the reservoir. Evaluation was conducted through in situ algal bioassay experiments (in situ ABEs) using the cubitainer setting in the reservoirs. For in situ ABEs, we compared and analyzed variations in chlorophyll-a (CHL-a) and phosphorus concentrations in Boryeong Reservoir before and after the water tunnel construction. We then analyzed the nutrient effects on the reservoir. Analysis for nitrogen and phosphorus was done in the three locations of the reservoir and two locations of the ABEs. The in situ ABEs results showed that phosphorous and Nitrogen, the primary limiting nutrient regulating the algal biomass was not limited in the system. The treatments of phosphorus or simultaneous treatments of N+P showed greater algal growth than in the control of nitrate-treatments, indicating a phosphorus deficiency on the phytoplankton growth in the system. The water from the Geum River had 5 times higher total phosphorus (TP) than the water in the reservoir. Efficient management is required as pumping of the river water from Geum River may accelerate the eutrophication of the reservoir.

Cyanobacteria Aphanizomenon population is widely distributed in the world, and well known as harmful algae by producing toxins and off-flavor materials, thus belonging to one of the taxa that became more interested in the field of limnoecology. In this study, the frequency, intensity, and duration of Aphanizomenon occurrence were increased with the abnormal drawdown of water level in the winter in Boryeong Reservoir, and the spatial and temporal characteristics of them are compared with each other in the perspective of hydrometeorology (1998 to 2017) and limnology (2010 to 2017). In Korea, Aphanizomenon flourished mainly in high temperature, and the appearance in the low temperature was rare in total five times. The harmful cyanobacteria Aphanizomenon was observed in the low temperature (December to February) in Boryeong Reservoir from 2014, and then reached a maximum value of 2,160 cells mL-1 in January 2017. In addition, the period exceeding 1,000 cells mL-1 at this time was more than 3 months. This was simultaneously associated with abnormal water level fluctuation in the low temperature (<10℃). The large drawdown of water level in the winter season has the potential to promote or amplify the germination and development of harmful algae. Also, subsequent water quality and ecological impacts (e.g., algal toxins and off-flavor substances) need to be considered carefully.