An ecologist’s view: ecological regime shift and needs for adaptive management
According to literature in theoretical ecology, alternative stable states exist in lake ecosystems because ecosystem responses to environmental factors are nonlinear (Carpenter 2003, p.179; Lewontin 1969, pp.13–24). In shallow eutrophic lakes, there are “turbid states” and “clear states” in which phytoplankton and submerged macrophytes dominate, respectively. When the effect of an environmental change is greater than a certain threshold, a regime shift to another state occurs. Moreover, in the turbid state, when phytoplankton dominates, light cannot penetrate to the bottom of the lake, which causes aquatic plants to die and increases the populations of invertebrates, Cyprinidae fish planktivores, and smaller sized zooplankton that maintains the lake in a turbid state.
In the clear state, aquatic plants dominate, and plant roots restrain the resuspension of mud during wind events. Submerged macrophytes compete with phytoplankton for nutrients and release some allelochemicals, thereby inhibiting the growth of phytoplankton. Many attached aquatic microorganisms obtain food and shelter from the macrophytes and some decompose senescent macrophytes, which increases lake transparency (Jeppesen et al. 1998, p.423). Hence, it is theoretically difficult to achieve a utopian-like condition—the clear water that many residents prefer does not sustain large fish populations.
To complicate things further, global warming and climate change have caused unprecedented events that affect clear water states, such as increased temperatures and rainfall, violent typhoons, and phytoplankton blooming in the north basin, which now practically occurs annually. Due to drastic environmental fluctuations, the lake can easily return to a “turbid state.”
In recent years, “adaptive management” has increasingly been applied to the management of ecosystems under uncertain conditions (Allen et al. 2012, pp. 3342–3357). In adaptive management, the strategy may be changed by the feedback from monitored results. In the case of overgrown macrophytes in Lake Biwa, since the prefectural program has not yielded enough profit to warrant a business, it will not be practical to continuously provide for a mowing budget in the future (see also Sect. 3.3). However, the cost of burning mown weeds and handling wastes is slightly decreased by composting. Therefore, an adaptive management system to discover a threshold value for regime shift is needed (Ishikawa et al. 2019, pp. 69–82; Ishikawa et al. 2020, pp. 577–581).
Interviews and actor analysis revealed a multi-actor situation
We conducted interviews with approximately 30 local actors identified by practitioners. Interviewees included officers of the Lake Biwa Environmental Conservation Division of Shiga Prefectural Government and environmental departments of Ōtsu and Moriyama cities, local inhabitants, farmers, fisherfolk, student volunteers, businesspeople, and social entrepreneurs. Interviews mainly focused on the overgrown weed problem, but related topics and thoughts on their living and/or working situations were also discussed extemporaneously. Also, 80 local inhabitants were interviewed about the usage of composted weeds on the occasion of free distribution in February 2018. The results of interviews were crosschecked with participatory observations at meetings, workshops, and field events associated with the overgrown weed problem. Based on these interviews and observations, local actors were qualitatively classified as discussed below.
Different perceptions among actors
The interviews revealed that the perception and understanding of the weed problem differed among actors, although they shared the recognition that it was a wicked socio-ecological problem (Fig. 5). The prefectural government is responsible for lake conservation and addressed the problem of overgrown aquatic weeds in terms of ecosystem management, which was also emphasized by ecologists as discussed in the previous subsection. In contrast, coastal inhabitants and municipality officers tended to regard this issue as a social problem of unpleasant odor and waste, which were perceived as a nuisance.
In addition to local governments and coastal inhabitants, local fisherfolk and student volunteers were identified as stakeholders. For fisherfolk, aquatic weeds were a sign of a good fishing place, just as they were in the Edo period (see Sect. 3.4). However, catch of endemic species, such as Carassius buergeri grandoculis (nigoro-buna locally) and Gnathopogon caerulescens (hon-moroko), drastically decreased. In recent years, fisherfolk have contributed to the prefecture’s program by removing aquatic weeds (Fig. 1c).
Meanwhile, a non-profit student organization, called the International Students Volunteer Association, coordinated an annual conservation event to remove designated alien weeds such as Ludwigia grandiflora subsp grandiflora (ōbana-mizukinbai), with some hundred participants. Students participated for fun and networking. They shared information on the ecological issues of alien weeds in Lake Biwa in a pre-event briefing, and local governments provided logistical support, such as waste pick-up.
In addition, a local company funded by the prefectural government commercialized composted weeds as a product. The funding program also supported a local craft shop to use dried and milled weeds for the coloring of glasswork. A flower shop in Ōtsu sold herb kits with composted weeds. Furthermore, a confectionery started using composted weeds to grow plants for shop display.
Personal activities and launch of a civic group
Interviews also identified some local individuals who had been personally clearing washed weeds from the shore. For instance, an individual (Y-san) has been cleaning Manohama beach in front of his guesthouse in Katata, Ōtsu, every morning alone (Fig. 4a) since 2014, and sharing dried weeds with those who desired them since 2016. Neighboring residents, including M-san, received weeds for their home gardens to grow vegetables for family consumption. These activities were undertaken for their own purposes (ikigai) and did not count as ecological conservation. Y-san stated, “I did nothing. I just cleaned up the beach in front of my home.” M-san said, “I do not know the aquatic weed problem well as we are just growing vegetables.”
Y-san posted online about beach cleaning and almost daily. W-san, an environmental sociologist in residence, recognized Y-san through these daily posts. W-san also knew of a local corporate executive, K-san, who proposed an idea to acknowledge and circulate “a goodwill” to Lake Biwa (a prototype of the Biwa Point presented later). W-san invited Y-san and K-san to establish a civic group called Suihōzan (meaning aquatic weeds are a gold mine), launched in late 2017 (Wakita et al. 2020, pp. 203–212).
One of the authors (Fujisawa) also joined this group. He has participated in civic projects in collaboration with Ōtsu City before. Fujisawa suggested submitting a proposal on “the civic actions to develop a social system to reuse aquatic weeds in Lake Biwa as resources” with Ōtsu City to a social innovation contest, Challenge Open Governance 2017. This proposal was nominated as a finalist for the award. Through this proposal, Suihōzan became a fundamental organization to address the overgrown weed problem, strengthened by the potential of civic collaboration with local governments in the cities of the south basin area.
Questionnaire survey highlighted less engaged actors
In addition to the aforementioned “active” actors, there was a “small-voice” majority living in urbanized areas. In January 2018, a postal questionnaire survey was conducted in the three municipalities in the south basin area, namely Ōtsu (southern part only), Kusatsu, and Moriyama, to investigate (1) to what degree inhabitants were aware of the presence of and heaviness of aquatic weeds in Lake Biwa, and (2) how they evaluated the measures to tackle this socio-ecological problem. The survey sheets were mailed to 30,203 households in 78 randomly sampled postal code areas. Of those, 4,578 households responded (response rate: 15.1%). The age group of respondents was biased towards elder generations (57.6% were 60 years old or older) in comparison with the actual demography of the study area, because household heads were asked to respond. The gender balance (49.8%, male; 49.5%, female) was close to that of the actual demography.
Most respondents recognized that overgrown aquatic weeds (1) created an unpleasant odor, (2) blemished lake views, (3) degraded the water quality, and (4) caused undesirable effects on aquatic organisms and fisheries. Since local print and broadcast media had run stories on the weed problem, even respondents who did not live near Lake Biwa and seldom visited the lakeshore were cognizant of the ongoing issues (Fig. 6). In addition, 91.4% of the respondents thought that they benefited from the ecosystem of Lake Biwa, while 67.2% thought that public authorities should measure alien fish populations (asked as a proxy of environmental problem measurements).
Regarding the measurement program coordinated by Shiga Prefectural Government (see Sect. 1), 78.4% of respondents recognized that the prefectural government removed aquatic weeds, while fewer respondents were knowledgeable of the production of composted weeds (46.4%), free distribution of composted weeds (19.5%), and developing technologies to prevent the overgrowth of weeds (23.0%; see Fig. 7).
Further, inhabitants’ priorities regarding governmental actions concerning the aquatic weed problems were different from their recognition rates. Their top priority was mowing, and their second priority was technological development to prevent overgrowth, followed by the free distribution of composted weeds. This indicates that overgrowth prevention was more important for inhabitants than effective reuse.
Willingness to pay for aquatic weed measures
In addition to public awareness, the cost–benefit balance of environmental conservation cannot be ignored. Since the prefectural government spends 600 million yen per year on the conservation program, the cost–benefit balance of the budget was evaluated from the viewpoint of the inhabitants. The social benefit of measures tackling overgrown weeds was analyzed using the contingent valuation method, which is universally applied in environmental economics to derive the willingness to pay (WTP) for environmental changes (Phaneuf and Requate 2016, pp. 576–579).
The dichotomous choice format was applied to elicit respondents’ WTP as follows. First, respondents were asked to answer the hypothesized question “would you be willing to pay X yen per year for the environmental conservation to mow overgrown weeds, compost them for free distribution, and support the development of new technologies to prevent the overgrowth of weeds in Lake Biwa?” where X was the presented bid amount, randomly set to 100, 300, 500, 1000, 2000, 3000, or 5000 yen. Second, the probability of “yes” was calculated against the hypothesized question by the bid amount Xs, excluding resisted answers. Then, a WTP was obtained by multiplying the bid amounts by the corresponding probabilities of “yes” (Fig. 8). Finally, mean WTP was obtained by integrating the probability “yes” function from X = 0 to Xmax where probability “yes” equals zero.
It was anticipated that the probability “yes” would get to zero at X = 5000 at the stage of setting bid amounts. However, the probability “yes” was much higher than zero, equaling 0.278, at X = 5000. Therefore, the mean WTP was underestimated. Taking this limitation into account, the mean WTP was calculated by truncating the probability “yes” distribution at 5000 yen, totaling 2879 yen for the mean WTP per household. This value was slightly higher than the average household expenditure for a weekend leisure activity in the Lake Biwa area (2806 yen). Since the study area had approximately 240,000 households in total, 690 million yen would be collected annually for the measures directed against overgrown weeds. This estimate was higher than the total cost of the actual conservation program (see Sect. 1). It should be noted that income effects and lack of knowledge of preferences might affect the estimates (but see Sect. 5.3).
This cost–benefit analysis supported the environmental conservation program of the prefectural government. However, the value placed on the overgrown weeds varied among local inhabitants, as well as the economic and psychological damages. Different values may result from different priorities within the conservation program. Therefore, if the government were to plan an environmental tax, it would be difficult to even the tax burden based on the beneficiary liability principle. A more effective way to involve local inhabitants and other marginalized actors in decision-making is required.
Aquatic weeds in Lake Biwa three hundred years ago: a historical foundation
In addition to these “present” actors, “past” actors in the historical context were also identified. Historically, aquatic weeds have long been indispensable natural resources for the human subsistence economy, being used as organic fertilizer, and exploited for popular fishing places, due to their propensity to serve as spawning and nursery grounds for fish. Historical documents evidenced that aquatic weeds were already in high demand by the early eighteenth century (middle Edo period), although the agro-economic value of aquatic weeds sharply declined in the mid-1950s when chemical fertilizers were introduced (Hiratsuka et al. 2006, p. 94).
Disputes over weed exploitation in the 1700s
According to an old document possessed by Kanda Jinja (shrine), Ōtsu, a dispute concerning rights over mowing aquatic weeds (called mogusa at that time) took place in present-day Ōtsu in 1701. Ichiemon, an inhabitant of Ōtsu Kitaho-chō, filed a suit against the fisherfolk of Honkatata-mura, a coastal village that was part of present-day Katata, Ōtsu. The fisherfolk of Honkatata-mura had collected aquatic weeds in the fishing area over which Ichiemon’s family had enjoyed exclusive rights for several generations.
According to Ichiemon, a previous intrusion had concluded with a verbal negotiation between him and the fisherfolk. However, he instituted a new suit against the fisherfolk because they had again intruded into his fishing area. Refuting Ichiemon’s arguments, the fisherfolk stated two reasons why they should be allowed to use the fishing area: (1) “we have fishing rights over the entirety of Lake Biwa,” and (2) “there was a dispute twenty-five years ago as well, and our rights were approved then.”
This conflict ran as follows: The fisherfolk from Honkatata-mura had been collecting aquatic weeds for farmers to use as fertilizer. For this reason, farmers from Honkatata-mura and the neighboring Imakatata-mura joined the dispute in support of the fisherfolk. Consequently, Honkatata-mura and Imakatata-mura won the suit and acquired the rights to continue collecting aquatic weeds.
Local traditional knowledge about aquatic weeds
Local people during the Edo period possessed indigenous knowledge about the agricultural efficacy of aquatic weeds. In one of the documents exchanged during the dispute over weed exploitation, one excerpt described aquatic weeds as “nourishment for rice paddies and fields,” constituting an agricultural fertilizer. This fact indicates that aquatic weeds were already being used as fertilizer at the beginning of the 1700s.
The same document also mentioned that aquatic weeds were used “because there were no grassy hills or meadows in the village.” This suggests that local people regarded aquatic weeds as a lower-quality fertilizer than grass obtained from grassy hills and meadows. Nevertheless, the fact that two villages cooperated to win the rights over aquatic weeds indicates that weeds were a valuable resource for fertilizer, especially for lakeside villages that could produce no other fertilizers of their own.
Ōtsu was already an urbanized area, called “Ōtsu-hyakuchō” (hyakuchō roughly means “a hundred town sections”). As such, the wastewater from Ōtsu created a eutrophic condition for aquatic weeds that was favorable for the fisherfolk of Honkatata-mura. It appears that local people at that time had certain knowledge about the conditions of aquatic weed growth and management, as one of the documents recorded fisherfolk from Honkatata-mura explaining that “wastewater from Ōtsu grows aquatic weeds well.”