We analyze the efficacy of using a Do-It-Yourself (DIY) modular instrument to estimate the diffuse attenuation coefficient (K_d) of photosynthetically active radiation (PAR), which can be used for operational oceanography in turbid shallow waters. This parameter evaluates the water transparency, as it summarizes several water components providing an indicator for water quality. Historically, water transparency has been measured with a simple and inexpensive tool: the Secchi disk. Although it contributes a valuable index of visual water clarity, the quality of its measurements is user-dependent, and it does not enable the automatic monitoring of the water quality. For this reason, we need electronic devices to get accurate measures and facilitate long-term evaluations for water quality monitoring. This paper has two main objectives: First, to present the KduPRO, a low-cost and DIY moored instrument. The KduPRO is an evolution of the KdUINO buoy, that provides an estimation of the water transparency in coastal areas and continental waters, with an automatic quality control parameter that makes this sensor suitable for operational observing systems; and second, to provide a replicability analysis associated to the uncertainty of its K_d estimations. This instrument is based on a modular system of light sensors, independent of each other, measuring the irradiance at different depths. This study analyses the performance of the KduPRO with other reference commercial instruments, the performance between different modules of the same system and finally, a case study of measuring the water quality in Loch Leven (a lake in Scotland). The affordable cost, ease of use and measurement repeatability make this instrument a potentially valuable tool for anyone interested in monitoring water quality.

Measuring the diffuse attenuation coefficient ($K_d$) allows for monitoring the water body’s environmental status. This parameter is of particular interest in water quality monitoring programs because it quantifies the presence of light and the euphotic zone’s depth. Citizen scientists can meaningfully contribute by monitoring water quality, complementing traditional methods by reducing monitoring costs and significantly improving data coverage, empowering and supporting decision-making. However, the quality of the acquisition of in situ underwater irradiance measurements has some limitations, especially in areas where stratification phenomena occur in the first meters of depth. This vertical layering introduces a gradient of properties in the vertical direction, affecting the associated $K_d$. To detect and characterize these variations of $K_d$ in the water column, it needs a system of optical sensors, ideally placed in a range of a few cm, improving the low vertical accuracy. Despite that, the problem of self-shading on the instrumentation becomes critical. Here, we introduce a new concept that aims to improve the vertical accuracy of the irradiance measurements: the underwater annular irradiance ($E_a$). This new concept consists of measuring the irradiance in an annular-shaped distribution. We first compute the optimal annular angle that avoids self-shading and maximizes the light captured by the sensors. Second, we use different scenarios of water types, solar zenith angle, and cloud coverage to assess the robustness of the corresponding diffuse attenuation coefficient, $K_a$. Finally, we derive empirical functions for computing $K_d$ from $K_a$. This new concept opens the possibility to a new generation of optical sensors in an annular-shaped distribution which is expected to (a) increase the vertical resolution of the irradiance measurements and (b) be easy to deploy and maintain and thus to be more suitable for citizen scientists.

Citizen science platforms (CSPs) and citizen observatories (COs) are rapidly expanding research infrastructures (RIs) that support the growth of citizen science. These systems have boosted data collection capabilities and broadened participant engagement across spatial and demographic dimensions. Despite their essential role in advancing citizen science, the current state of knowledge of these infrastructures remains largely unexplored, affecting both theoretical understanding and practical implementation. The study discussed herein addresses this knowledge gap through a systematic review of 474 articles, with in-depth analysis of 72 publications spanning a 15-year period across multiple disciplinary domains. The methodological framework integrates bibliometric analysis with qualitative investigation, utilizing Web of Science and Scopus databases, supplemented by grey literature from Zenodo and Google Scholar. Findings indicate that research in this field has developed across three main waves: technological development and engagement, monitoring systems and openness, and frontiers technologies. This evolution reflects a progression in the CSP body of knowledge from technical documentation to complex socio-technological systems. Analysis of 450 articles identified 98 unique terms referring to CSPs, highlighting conceptual fragmentation. To clarify the landscape of overlapping, we propose a CSP purpose-based taxonomic framework comprising nine platform categories, contributing to a clearer understanding of the CSPs’ role in citizen science. Additionally, our systematic analysis reveals key research trajectories essential for strengthening CSPs and COs as sustainable infrastructures.

BioBlitzes are widely used citizen science events that combine biodiversity monitoring, public participation, and environmental awareness through short and intensive observation campaigns. However, applying this model to marine environments presents additional challenges related to safety, access, weather dependency, specialised equipment, species identification, and sustained participation. This paper presents the BioMARathon model as a case study of how BioBlitz-inspired events can be adapted to marine citizen science contexts. The BioMARathon extends the conventional BioBlitz format into a longer, seasonal, and distributed engagement model designed specifically for marine and coastal environments. The paper describes the conceptual foundations of the model in the Janus Engagement Framework, which informed both the design of the BioMARathon and the adaptation of the MINKA citizen science observatory to better support participation, validation, feedback, and continuity over time. BioMARató Catalunya, launched in 2021, is presented as the founding implementation of the model and as the basis for later replication in Portugal. Between 2021 and 2025, BioMARató Catalunya showed continued growth in participation, observations, and taxonomic coverage, while also contributing to the detection of non-indigenous species, first regional records, and climate-related ecological impacts. Beyond biodiversity outcomes, the case suggests that extending participation across a season, distributing activities through local mobilising organisations, and combining expert validation with visible feedback mechanisms can support recurrent participation, retention, and community reactivation in marine citizen science. Rather than offering a formal causal evaluation, this article contributes practical lessons for the design of citizen science initiatives in challenging environments.

Measuring water transparency allows us to monitor the water body's environmental status. One parameter to estimate water transparency is the light diffuse attenuation coefficient (Kd). This coefficient is of particular interest in water quality monitoring programs.The Kd describes the light extinction as function as the depth of downwelling irradiance, Ed. However, self-shading by the instrument itself can cause errors in Ed estimations. To avoid this effect, relative complex structures must be required to install the sensors that limit the vertical resolution of Ed measurements. Here we propose to use optical sensors in an annular-shape distribution to mitigate these limitations. For this, we introduce a new concept: the annular irradiance, Ea. We first compute the optimal angle to avoid self-shading while maximizing the light captured by the sensor. Second, we assess the robustness of the corresponding diffuse attenuation coefficient, Ka, in different scenarios of water types, solar angle and cloud coverage. Finally, we correlate Ka measurements with Kd at PAR region, and we derive empirical functions from translating Ka to Kd measurements.      This new coefficient is the basis of the new generation of the KdUINO instrument  (Bardaji et al., 2016) as a KduSTICK, which estimates the near-surface light extinction coefficient based on Ka measurements. Since the design of the instrument avoids self-shading, the device is expected to be particularly useful in those underwater environments where high vertical Ed resolution is required.Furthermore, instruments based on this light-sensing approach are much simpler to deploy and maintain, and it is possible to design low-cost and Do-It-Yourself (DIY) versions. All these features facilitate its use for non-academic users, making the KduSTICK an optimal instrument to be used in Citizen Science water quality monitoring programs.