Lake Izunuma Research Articles

Survey of freshwater mussels using high‐resolution acoustic imaging sonar and deep learning‐based object detection in Lake Izunuma, Japan

Abstract The use of traditional in situ methods for underwater surveys to map freshwater mussel habitats is limited by challenges such as water transparency, depth and high labour demands. In this study, adaptive resolution imaging sonar (ARIS) was applied to monitor mussel distribution and abundance. In contrast to conventional quadrat surveys, this acoustic survey is non‐invasive and enables direct observation of mussels to allow their survival status to be determined in turbid water. ARIS produces high‐quality acoustic images that facilitate the creation of a distribution map for broader‐scale monitoring, especially if paired with deep learning methods such as the YOLOv4 algorithm for automatic mussel detection and classification. ARIS was successfully applied to surveying over 2000 m2 of Lake Izunuma in Miyagi, Japan. In one site, a high mussel abundance of ~0.6 individuals/m2 was detected, while other sites had low densities. The detection model achieved a mean average precision of 0.97. The survey results were used to generate a distribution map of living mussels. This study illustrates the feasibility of using an acoustic video camera with an open‐source deep learning algorithm to monitor mussels and other benthos in turbid water.

Redescription of <i>Argulus mongolianus</i> (Crustacea: Branchiura: Argulidae), an Ectoparasite of Freshwater Fishes in East Asia, with Its First Record from Japan

Both adult females and males of Argulus mongolianus Tokioka, 1939 were collected from the buccal cavity wall and body surface of freshwater fishes in Lake Izunuma and Lake Uchinuma, Miyagi Prefecture, northen Honshu, Japan. The original description of the species was insufficient, based on a single female from Inner Mongolia, China, and no further description has been made to date. Thus, this paper redescribes A. mongolianus based on the newly-collected specimens, including the first description of the male. This represents the first record of A. mongolianus from Japan. The infected fishes were largemouth bass, Micropterus salmoides (Lacepède, 1802), common carp, Cyprinus carpio Linnaeus, 1758, Japanese white crucian carp, Carassius cuvieri Temminck and Schlegel, 1846, and silver crucian carp, Carassius sp. The three species other than common carp are new host records for A. mongolianus. This parasite was most probably introduced with an unspecified freshwater fish from China into Japan.

A record of Eichhornia crassipes (Mart.) Solms from Lake Izunuma, Miyagi Prefecture, Japan and the possibility of its establishment due to global warming

A record of <i>Eichhornia crassipes</i> (Mart.) Solms from Lake Izunuma, Miyagi Prefecture, Japan and the possibility of its establishment due to global warming

Seasonal occurrences, reproductive seasons, and habitat environments of an endangered damselfly Paracercion plagiosum (Odonata: Coenagrionidae) in ponds neighboring Lake Izunuma–Uchinuma, Japan

Seasonal occurrences, reproductive seasons, and habitat environments of an endangered damselfly <i>Paracercion plagiosum</i> (Odonata: Coenagrionidae) in ponds neighboring Lake Izunuma–Uchinuma, Japan

Hydrodynamic‐Driven Changes in the Source and Composition of Sedimentary Organic Matter via Grain Size Distribution in Shallow Lakes

AbstractSediment organic matter (SOM) differs in composition and function in different size fractions in relation to material and energy flows. The hydrodynamic effects on a lake's autochthonous (terrestrial plants) and allochthonous (microalgae, aquatic plants, and bacteria) inputs and transformation, and the components of SOM are still far from clear. To elucidate the SOM composition as driven by the hydrodynamic conditions associated with sedimentary grain size, we performed an ecosystem‐level investigation in the shallow lake Izunuma, Japan, measuring source‐specific fatty acids and the current velocity. High organic matter concentrations occurred in the finer fractions. Bacteria were dominant in the &lt;32 μm fraction, microalgae were mainly present in the &lt;32 and 63–125 μm fractions, aquatic plants appeared to be evenly distributed in all size fractions, and terrestrial plants mainly comprised the &gt;125 μm fraction. Although the linear correlation between current velocity and sedimentary total organic carbon (TOC) was not statistically significant, the relationship between current velocity frequency and sedimentary TOC was significant. The highest Pearson coefficient occurred at a current velocity of 6 cm/s in sand. The relationship between allochthonous inputs and current velocity frequency was similar to that of TOC. Autochthonous organics had the greatest coefficient with two peaks at 4.5 and 8 cm/s. The threshold for sand resuspension varied with organic sources, while this phenomenon was absent in cohesive mud. Hydrodynamic forces affected the grain size of sediments and drove the gradient distribution of the SOM sources, which should be considered when managing freshwater lakes in light of future climate change.

Semiaquatic spiders Alopecosa cinnameopilosa rely on prey derived from macrophyte‐based food web: evidence from Lake Izunuma, Japan

Although lacustrine food webs have been extensively studied, food webs formed on floating-leaved macrophytes are poorly understood. In recent years, lotus Nelumbo nucifera, which was often seen in shallow waters, has rapidly expanded and covered a significant part of the surface of the eutrophic shallow Lake Izunuma in Japan. We investigated the diet of the semiaquatic spider Alopecosa cinnameopilosa collected from lotus vegetation and the shore, using carbon and nitrogen stable isotopes. We categorized the spiders’ potential diet as aquatic prey (aquatic insects and small fish), terrestrial insects, or semiaquatic leaf beetles (Donacia provostii and Galerucella nipponensis) that forage mainly on floating-leaved macrophytes. In lotus vegetation, A. cinnameopilosa relied mostly on leaf beetles (mean dietary contribution: 57.3% in July and 46.0% in September). On the lake shore, A. cinnameopilosa relied on both leaf beetles (41.0%) and aquatic prey (36.4%) in July, whereas they relied mostly on aquatic prey (83.1%) in September. The difference in diets between sites could reflect differences between sites in the abundance of leaf beetles. Therefore, macrophyte-based food webs that start from lotus or water chestnuts could significantly support semiaquatic spiders on macrophyte vegetation in Lake Izunuma.

Feasibility study of monitoring using UAV for egrets in Lake Izunuma.

Feasibility study of monitoring using UAV for egrets in Lake Izunuma.

Development of a Small Electric Robot Boat for Mowing Aquatic Weeds

HighlightsA small, automatically guided electric robot boat was developed to control the growth of aquatic plants in lakes.The robot boat was able to mow without becoming entangled with aquatic plants due to the paddle propulsion mechanism.The average speed was 0.41 m s-1, and the lateral deviation from the set path was 9.4 cm.The growth restraint effect was confirmed using aerial images collected by a drone.Abstract. At present, aquatic plants are becoming a problem in various lakes. Aquatic weeds that grow to high densities cause decreases in the oxygen concentration in the water, accumulation of sludge, and adverse effects on water use facilities and fisheries. Although there are large machines for cutting and harvesting aquatic plants, their use is limited due to their high cost, large size, and heavy weight. On the other hand, manual cutting is very labor intensive and inefficient. Therefore, in this research, we developed a labor-saving and low-cost robot boat to mow aquatic plants. This robot boat is automatically controlled by a real-time kinematic global navigational satellite system (RTK-GNSS) and is characterized by its small size, light weight, excellent portability, and low energy consumption. In addition, a paddle mechanism that replaces a conventional propeller was introduced as a propulsion mechanism to prevent entanglement of water plants and enable long-term automatic navigation. Mowing lotus (Nelumbo nucifera) in Lake Izunuma, Miyagi prefecture, Japan, confirmed that mowing could be properly conducted with a lateral deviation of 9.4 cm, average speed of 0.41 m s-1, and average power consumption of 518 W even when lotus was at its densest growth. If the cutting width of the robot boat was 1.2 m and the sidelap width was 0.3 m, the theoretical field work rate would be 0.133 ha h-1. Images captured by a drone confirmed that cutting with the robot boat was effective in suppressing the growth of lotus. It was found that the effect of suppressing growth was maximized by mowing at the time when the stopping leaves appeared in the late growth stage of lotus. Keywords: Autonomous navigation, Lotus, Moving baseline, Robot operation system, RTK-GNSS, Virtual private network.

Dietary analysis of introduced carnivorous snakehead Channa argus in Lake Izunuma using carbon and nitrogen stable isotopes

Dietary analysis of introduced carnivorous snakehead <i>Channa argus</i> in Lake Izunuma using carbon and nitrogen stable isotopes

Approach deliberation for source identification of sedimentary organic matters via comparing freshwater lakes with multi-ecotypes

Despite of the importance of understanding the sediment quality for lacustrine management, the source evaluation of sedimentary organic matter (SOM) in freshwater lakes is still insufficient. In this study, two shallow eutrophic lakes of Lake Taihu, China and Lake Izunuma, Japan were systematically investigated. Results of fatty acid profiles demonstrated that a wide range of organic matters, varying ecotypically, was inputted into the sediments of both lakes. Interestingly, there was a strong contribution from terrestrial plants to the sediments across ecotypes, with an approximate input from bacteria, and a relatively minor input from microalgae mainly included cyanobacteria, green algae, diatom and dinoflagellates. In addition, isotopic mixing model depicted a complementary picture that a significant, but spatially variable, amount of organic matter was derived from emergent and floating-leaf plants of Phragmites, Nelumbo, Nymphoides and Trapa L in Lake Izunuma. A general indicator selection procedure for the source assignments of SOM in freshwater ecosystems was therefore proposed: fatty acids could be a valid biomarker when the potential sources are unknown or unavailable; stable isotopes could be an effective supplement approach when assessing the special or defined organic sources.

Hypoxia within macrophyte vegetation limits the use of methane-derived carbon by larval chironomids in a shallow temperate eutrophic lake

Methane-derived carbon (MDC) can subsidize lake food webs. However, the trophic transfer of MDC to consumers within macrophyte vegetation is largely unknown. We investigated the seasonality of δ13C in larval chironomids within Nelumbo nucifera (Gaertn.) and Trapa natans var. Japonica (Nakai) vegetation in the shallow, eutrophic Lake Izunuma in Japan. Over the past several years, N. nucifera has rapidly expanded across more than 80% of the lake surface. Prior to the expansion of N. nucifera (2007–2008), a previous study reported extremely low larval δ13C levels with peak sediment methane concentrations in August or September. After the expansion of N. nucifera (2014–2015), we observed extreme hypoxia as low as or lower than 1 mg l−1 among the macrophyte coverage during June and August. During August and September, no larvae could be found among N. nucifera, and larvae in T. natans showed relatively high δ13C levels (> − 40‰). In contrast, larvae were markedly 13C–depleted (down to − 60‰) during October and November. The renewed supply of oxygen to the lake bottom may stimulate MOB activity, leading to an increase in larval assimilation of MDC. Our results suggest that macrophyte vegetation can affect the seasonality of MDC transfer to benthic consumers under hypoxic conditions in summer.

伊豆沼・内沼周辺で秋季に採集されたユスリカ成虫 （双翅目: ユスリカ科）

伊豆沼・内沼周辺で秋季に採集されたユスリカ成虫 （双翅目: ユスリカ科）

伊豆沼において土壌シードバンクから出現した絶滅危惧種ムサシモ（Najas ancistrocarpa，イバラモ科）

伊豆沼において土壌シードバンクから出現した絶滅危惧種ムサシモ（Najas ancistrocarpa，イバラモ科）

Trophic transfer of methane-derived carbon to zooplankton in eutrophic shallow lake Izunuma inferred from carbon stable isotope analysis

Trophic transfer of methane-derived carbon to zooplankton in eutrophic shallow lake Izunuma inferred from carbon stable isotope analysis

Ontogenetic dietary shifts of largemouth bass do not increase trophic position in a shallow eutrophic lake in Japan

The trophic positions of top predators can provide useful information for estimating the length of food chains and for assessing the impacts of invasive species or the bioaccumulation of harmful compounds. In aquatic ecosystems, large carnivorous fishes may change their trophic positions ontogenetically. We used stable carbon and nitrogen isotope ratios to test the hypothesis that the trophic positions of largemouth bass, top predators in Lake Izunuma, Japan, would increase with total length (TL) as a result of ontogenetic shifts in diet. Results from a stable isotope analysis in R mixing model indicated that largemouth bass were a major food source for largemouth bass ≥200 mm TL. However, the trophic positions of largemouth bass did not increase with the dietary shift from zooplanktivory to piscivory, and actually decreased when larger fish shifted towards feeding on red swamp crayfish. In Lake Izunuma, the trophic positions of small omnivorous fishes and red swamp crayfish were not higher than those of zooplankton. This explains why the largest largemouth bass occupied lower trophic positions than smaller individuals. Our results suggest that the body size of carnivorous fishes should be taken into consideration when using their trophic positions as top predators to evaluate aquatic systems.

Zoobenthos are minor dietary components of small omnivorous fishes in a shallow eutrophic lake

We examined whether small omnivorous fishes (smaller than ~100mm long) integrate littoral, pelagic and benthic pathways in a shallow, eutrophic lake (Lake Izunuma, Japan). The surface of the lake was covered by a dense vegetation of floating-leaved macrophytes, and small species dominated the icthyofauna. We determined the δ13C and δ15N ratios of five dominant species of small omnivorous fishes. Using a stable isotope analysis in the R mixing model, we determined the possible contribution of three potential food sources (epiphytic algae, zooplankton and zoobenthos (larval chironomids)) to omnivorous fish tissue compositions. Four omnivorous fishes (Gnathopogon elongatus elongatus, Pseudorasbora parva, Biwia zezera and Tridentiger obscurus) subsisted largely on epiphytic algae and zooplankton, whereas zoobenthos contributed little to their diets. Acheilognathus rhombeus subsisted mostly on epiphytic algae. Thus, in this shallow, eutrophic lake, omnivorous fishes incorporated both littoral and pelagic production into the food web, but rarely benthic production. The dominant benthic chironomid larvae often burrow several centimetres into the sediment, and the low dietary contribution of zoobenthos to small fishes may be due to inefficiency at foraging on buried benthos associated with fish body size.

Assessing the biological process of Hydrilla verticillata predation in a eutrophic pond using high-resolution acoustic imaging sonar

Most Hydrilla verticillata disappeared soon after planting in unsuccessful restoration efforts carried out at Lake Izunuma (northeastern Japan). Furthermore, the disappearance of aquatic plants has been speculated to be a result of crayfish predation. However, the precise cause remains unclear because of the low transparency of the lake water. In this study, to identify the source of Hydrilla verticillata predation and characterize the potential behaviors of predators, we used an acoustic monitoring system based on an image-processing program that we developed. A field experiment was performed in a small eutrophic pond adjacent to Lake Izunuma, and 24 Hydrilla verticillata were planted on the pond bottom. A DIDSON unit was mounted on an original frame with a 3° concentrator lens. Data were collected at 1.8 MHz and at a maximum range of 3.0 m. All Hydrilla verticillata disappeared within a day of planting. Using the image tracking approach, we estimated the walking speeds of two potential predators, namely crayfish (Procambarus clarkii) and pond snails (Cipangopaludina japonica), and distinguished them accordingly. Using this method, we identified crayfish as the main source of predation and characterized their foraging behavior in terms of the decreasing amount of Hydrilla verticillata. The foraging behavior of crayfish mostly ended after 17 h of planting, possibly because all plants had been eaten by that time.

Influence of hypoxia related to the expansion of lotus vegetation on benthic invertebrate community in Lake Izunuma

Influence of hypoxia related to the expansion of lotus vegetation on benthic invertebrate community in Lake Izunuma

Quantification of whooper swan damage to lotus habitats using high-resolution acoustic imaging sonar in Lake Izunuma, Japan

Conventional survey methods (e.g., surface surveys using optical video cameras and divers) have been widely used to detect aquatic plants and estimate their densities. However, these methods are affected by the transparency of water and observational skills of the divers and usually require considerable amounts of time for high-resolution sampling. We developed a new measurement system that combines a high-resolution acoustic imaging sonar, i.e., a Dual-frequency IDentification SONar (DIDSON) with a 1° concentrator lens, motion sensors, and GPS (global positioning system) receivers to quantify the underwater status and topography of a lake bottom effectively without the transparency of the water affecting the results. High-resolution spatial acoustic imaging was used for 3D visualization of the underwater status and bottom topography of a lake, and the numbers and depths of lotuses and bottom holes were estimated using the image processing program developed for this study. Our study revealed one specific aspect of the interaction between whooper swans foraging and the density of lotus (Nelumbo nucifera Gaertn.). The threshold water depth (approximately 1.3m) between high- and low-density areas was related to the body length of whooper swans.

流動と底質有機炭素の起源に注目した伊豆沼の底質形成機構の解析

流動と底質有機炭素の起源に注目した伊豆沼の底質形成機構の解析