Citation Beneficiaries of Discipline-Specific Mega-Journals: Who and How Much

The study examines how discipline-specific mega-journals (DSMJs)—large-volume, open access journals with soundness-only peer review—affect scholarly communication and evaluation through the citations they generate. Given disciplinary differences in publishing and citation practices, the authors focus on DSMJs within Environmental Sciences (ES). Citations underpin widely used evaluation metrics (e.g., Journal Impact Factor, cross-disciplinary influence, national impact) that inform journal selection, and institutional review, promotion, and tenure decisions. The authors conceptualize citations generated by DSMJs as “benefits” that are gained by cited journals, disciplines, and regions in citation-based evaluation systems. The research aims to fill a gap concerning DSMJs as distinct and significant sources of citations within specific fields. Research questions: (1) Who benefits and to what extent from DSMJs at the discipline/region level? (2) Within a specific discipline, which journals benefit from DSMJs and by how much?

Prior work defines mega-journals as high-output, broad-scope, OA journals with soundness-only peer review (Björk 2015) and discusses their growth, evaluation performance, and influence on scholarly communication (e.g., Solomon 2014; Wakeling et al. 2017; Kim and Park 2022). The JIF’s history, critique, and disciplinary differences are well documented (Larivière and Sugimoto 2019; Ioannidis and Thombs 2019), and citation-based indicators commonly inform assessments of journals, interdisciplinarity, and national impact (Borgman and Furner 2002; Truc 2022; Smith et al. 2014). The literature notes field-dependent citation behaviors and the diffusion of MJs across disciplines (Siler et al. 2020), while also highlighting concerns about over-optimization of metrics (Fire and Guestrin 2019) and the limited cross-field comparability of JIFs (e.g., Podlubny 2005; Van Leeuwen and Moed 2002). This study extends the literature by quantifying DSMJ-generated citation benefits across disciplines, regions, and within-discipline journals.

Study field and DSMJ selection: The Web of Science (WoS) category Environmental Sciences (ES) was chosen due to its large volume (126,235 citable items; JCR 2021). The five ES DSMJs with the highest 2021 outputs were analyzed: Sustainability, International Journal of Environmental Research and Public Health (IJERPH), Science of the Total Environment (STOTEN), Environmental Science and Pollution Research (ESPR), and Journal of Cleaner Production (JCP). In 2021 these five DSMJs published 43,210 articles citing 2,547,355 references (≈58.95 references per article). Data collection: From the WoS Core Collection (SCIE, SSCI, AHCI, ESCI), the authors retrieved articles published in 2021 in the five DSMJs and extracted their references, including author affiliations (for region analysis), WoS categories (for discipline analysis), and cited journal information. Year filters isolated references to items published in 2019–2021 for discipline and region analyses, consistent with JCR windows for JIF (2019–2020) and Immediacy Index (2021). To compute journal-level impacts, the cited set was matched to 13,725 journals with JCR data (total citations, article counts, citable items, 2021 JIF and Immediacy Index). Missing data led to exclusion of 4,658 journals for some analyses; 600,231 references (91.13% of 658,687) across 9,067 journals remained for discipline-level PCC analysis. Metrics and calculations: - JIF (2021) = citations in 2021 to items published in 2019–2020 divided by number of citable items in 2019–2020. - Immediacy Index (2021) = citations in 2021 to items published in 2021 divided by number of citable items in 2021. - DSMJ contribution to a journal’s JIF or II: share of that journal’s relevant 2021 citations that came from the five DSMJs (e.g., for Journal of Hazardous Materials, DSMJ contribution to 2021 JIF = E/F, where E = DSMJ citations in 2021 to 2019–2020 items and F = all 2021 citations to 2019–2020 items). - PCC (discipline level): citations in 2021 from the five DSMJs to journals in a WoS category (to items published 2019–2021) divided by all 2021 citations to items published 2019–2021 in those journals. For journals assigned to multiple categories, the “most representative” category (best JIF percentile) was used. - PCC (region level): DSMJ citations divided by all citations received by 2019–2021 items associated with the corresponding author’s region (from InCites; author position limited to “corresponding”). Region identification: Regions were determined by corresponding author address in WoS. Records lacking corresponding author address (9.6% of references) were removed from region analysis; multi-affiliation corresponding authors led to shared benefits across regions (6.1% of cases). Self- and intra-citation analysis: The authors separated DSMJ self-citations and intra-citations among the five DSMJs for items published in 2019–2021 and cited in 2021.

• Scale of DSMJ-generated citations: The five DSMJs made 658,687 citations to items published in 2019–2021, benefiting 13,725 cited journals. - Discipline distribution: DSMJ citations covered 247 of 254 WoS categories. By volume from DSMJs (Table 3): Environmental Sciences (ES) led with 148,102 citations (22.48% of DSMJ citations to top-20 categories), followed by Public, Environmental & Occupational Health (35,700; 5.42%), Green & Sustainable Science & Technology (34,221; 5.20%), Multidisciplinary Sciences (21,442; 3.26%), and Energy & Fuels (20,461; 3.11%). - Discipline-level contribution (PCC, Table 4; using 600,231 references over 9,067 journals): ES received 802,169 total citations in 2021 to 2019–2021 items, of which 147,042 came from DSMJs (PCC 18.33%). Environmental Studies had PCC 25.55%. Other notable PCCs: Water Resources 11.66%, Economics 9.16%, Management 7.18%, Toxicology 7.18%, Marine & Freshwater Biology 7.60%, Agricultural Engineering 10.59%. - Regional beneficiaries (Table 5): Of 634,669 regional citation benefits analyzed, Mainland China and the USA received 26.66% and 11.35% of DSMJ-generated citations, respectively. PCCs (DSMJ contributions to total regional citations across 2019–2021 items) were: Mainland China 0.92%, USA 0.50%, UK 0.83%, Italy 1.15%, Spain 1.59%, Australia 1.04%, India 0.77%, Germany 0.62%, Canada 0.80%, South Korea 0.78%, Iran 0.92%, Brazil 1.21%, Netherlands 0.88%, France 0.61%, Turkey 1.25%, Poland 1.25%, Japan 0.48%, Sweden 1.08%, Portugal 1.65%, Taiwan 1.03%. Average PCC across top regions ≈1.25%. - Journal-level impacts within ES: Immediacy Index (Table 6): Sustainability received 6,416 DSMJ citations to 2021 items, raising its 2021 II by 44.46%; ESPR received 4,524 DSMJ citations, increasing II by 60.81%. Other high DSMJ II contributions included Air Quality, Atmosphere and Health (82.73%) and Critical Reviews in Environmental Science and Technology (76.29%). JIF (Table 7): DSMJ contributions to 2021 JIF included Sustainability 31.17% (21,522 DSMJ citations to 2019–2020 items), JCP 25.71%, ESPR 23.87%, STOTEN 22.62%, Environmental Pollution 20.28%, Ecological Indicators 19.84%, Marine Pollution Bulletin 19.63%. In total, 15 ES journals had their 2021 JIF increased by more than 20% due to DSMJ citations. - Self- and intra-citations among DSMJs (Table 8; 2021 citations to 2019–2021 items): Self-citation shares were substantial: Sustainability 32.14% (22,188 self-citations), IJERPH 17.99%, STOTEN (22,093 self-citations), ESPR 23.28% (9,821), JCP 15.32% (15,241). Intra-citation shares from the other four DSMJs were also notable (e.g., JCP ≈15.16%). - Overall pattern: DSMJ citations exhibited wide disciplinary coverage but skewness toward ES and certain regions (notably Mainland China). DSMJ volume drives measurable increases in citation-based metrics (JIF and II) across a substantial set of journals within the discipline.

The findings show that DSMJs, by virtue of very high publication volume and extensive referencing, act as concentrated sources of citations that diffuse across many fields but disproportionately benefit Environmental Sciences and certain regions. This addresses the study’s questions by identifying who benefits (disciplines such as ES; regions including Mainland China, Spain, Turkey, Poland, Portugal; and many ES journals) and quantifying the extent (e.g., ES PCC 18.33%; multiple journals with >20% JIF contribution from DSMJs; large II boosts). The results imply that DSMJs influence bibliometric assessments beyond the mega-journals themselves, elevating citation-based metrics for traditional journals within the same field and, to a lesser extent, across fields. However, entities with already high overall citation volumes (e.g., large countries) may show modest PCCs despite high DSMJ citation shares because their total citation baselines are large, tempering the relative benefit. The disciplinary concentration of DSMJ diffusion suggests that citation-based evaluation systems may be biased in favor of fields with active DSMJs, complicating cross-field comparisons. More broadly, the inflation of citations from DSMJs raises concerns about relying on citation counts and derived indicators (JIF, II) as proxies for research quality and impact, reinforcing calls to contextualize or complement such metrics in evaluation practices.

Mega-journals are an established component of scholarly communication. This study quantified the influence of discipline-specific mega-journals (DSMJs) on citation-based evaluation at journal, discipline, and region levels. DSMJs generate broad yet skewed citation benefits, measurably boosting metrics such as JIF and Immediacy Index across many journals within Environmental Sciences and contributing nontrivially to the citation profiles of disciplines and regions. Given these effects, it is important to focus on improving the quality of academic exchanges, ensuring equitable distribution of benefits, and addressing critiques of citation-based assessment when interpreting or using such metrics.

• Region attribution was based solely on corresponding author affiliation, which may overlook contributions from co-authors and international collaborations; 9.6% of references lacked corresponding author address and were excluded from region analysis, and 6.1% involved multiple corresponding affiliations requiring shared attribution. - Missing data: 4,658 journals lacked complete JCR fields (JIF, II, citable items), resulting in their exclusion from some analyses; discipline-level PCC calculations used 600,231 references (91.13% of 658,687) across 9,067 journals. - Discipline assignment for multi-category journals was simplified to a single “most representative” category (best JIF percentile), which may affect category-level PCC estimates. - The study focuses on a single WoS category (Environmental Sciences) and one year (2021), limiting generalizability across disciplines and time. - Citation-based metrics do not necessarily reflect research quality; high DSMJ citation volumes may inflate indicators and introduce field-specific biases in evaluation.